Distinct roles for the two cGATA-1 finger domains

Two Isoforms of serpent Containing Either One or Two GATA Zinc Fingers Provide Functional Diversity During Drosophila Development

GATA transcription factors play crucial roles in various developmental processes in organisms ranging from flies to humans. In mammals, GATA factors are characterized by the presence of two highly conserved domains, the N-terminal (N-ZnF) and the C-terminal (C-ZnF) zinc fingers. The Drosophila GATA factor Serpent (Srp) is produced in different isoforms that contains either both N-ZnF and C-ZnF (SrpNC) or only the C-ZnF (SrpC). Here, we investigated the functional roles ensured by each of these isoforms during Drosophila development. Using the CRISPR/Cas9 technique, we generated new mutant fly lines deleted for one (ΔsrpNC) or the other (ΔsrpC) encoded isoform, and a third one with a single point mutation in the N-ZnF that alters its interaction with its cofactor, the Drosophila FOG homolog U-shaped (Ush). Analysis of these mutants revealed that the Srp zinc fingers are differentially required for Srp to fulfill its functions. While SrpC is essential for embryo to adult viability, SrpNC, which is the closest conserved isoform to that of vertebrates, is not. However, to ensure its specific functions in larval hematopoiesis and fertility, Srp requires the presence of both N- and C-ZnF (SrpNC) and interaction with its cofactor Ush. Our results also reveal that in vivo the presence of N-ZnF restricts rather than extends the ability of GATA factors to regulate the repertoire of C-ZnF bound target genes.

p66α Suppresses Breast Cancer Cell Growth and Migration by Acting as Co-Activator of p53

p66α is a GATA zinc finger domain-containing transcription factor that has been shown to be essential for gene silencing by participating in the NuRD complex. Several studies have suggested that p66α is a risk gene for a wide spectrum of diseases such as diabetes, schizophrenia, and breast cancer; however, its biological role has not been defined. Here, we report that p66α functions as a tumor suppressor to inhibit breast cancer cell growth and migration, evidenced by the fact that the depletion of p66α results in accelerated tumor growth and migration of breast cancer cells. Mechanistically, immunoprecipitation assays identify p66α as a p53-interacting protein that binds the DNA-binding domain of p53 molecule predominantly via its CR2 domain. Depletion of p66α in multiple breast cells results in decreased expression of p53 target genes, while over-expression of p66α results in increased expression of these target genes. Moreover, p66α promotes the transactivity of p53 by enhancing p53 binding at target promoters. Together, these findings demonstrate that p66α is a tumor suppressor by functioning as a co-activator of p53.

Evolution of Developmental GATA Factors in Nematodes

GATA transcription factors are found in animals, plants, and fungi. In animals, they have important developmental roles in controlling specification of cell identities and executing tissue-specific differentiation. The Phylum Nematoda is a diverse group of vermiform animals that inhabit ecological niches all over the world. Both free-living and parasitic species are known, including those that cause human infectious disease. To date, GATA factors in nematodes have been studied almost exclusively in the model system C. elegans and its close relatives. In this study, we use newly available sequences to identify GATA factors across the nematode phylum. We find that most species have fewer than six GATA factors, but some species have 10 or more. Comparisons of gene and protein structure suggest that there were at most two GATA factors at the base of the phylum, which expanded by duplication and modification to result in a core set of four factors. The high degree of structural similarity with the corresponding orthologues in C. elegans suggests that the nematode GATA factors share similar functions in development.

Specificity, redundancy and dosage thresholds among gata4/5/6 genes during zebrafish cardiogenesis

The Gata4/5/6 sub-family of zinc finger transcription factors regulate many aspects of cardiogenesis. However, critical roles in extra-embryonic endoderm also challenge comprehensive analysis during early mouse cardiogenesis, while zebrafish models have previously relied on knockdown assays. We generated targeted deletions to disrupt each gata4/5/6 gene in zebrafish and analyzed cardiac phenotypes in single, double and triple mutants. The analysis confirmed that loss of gata5 causes cardia bifida and validated functional redundancies for gata5/6 in cardiac precursor specification. Surprisingly, we discovered that gata4 is dispensable for early zebrafish development, while loss of one gata4 allele can suppress the bifid phenotype of the gata5 mutant. The gata4 mutants eventually develop an age-dependent cardiomyopathy. By combining combinations of mutant alleles, we show that cardiac specification depends primarily on an overall dosage of gata4/5/6 alleles rather than a specific gene. We also identify a specific role for gata6 in controlling ventricle morphogenesis through regulation of both the first and second heart field, while loss of both gata4/6 eliminates the ventricle. Thus, different developmental programs are dependent on total dosage, certain pairs, or specific gata4/5/6 genes during embryonic cardiogenesis.

This article has an associated First Person interview with the first author of the paper.

Summary: Targeted mutations were generated for each of the three gata4/5/6 genes in zebrafish to define functions for individual or combinations of these related transcription factors during cardiogenesis.

Analysis of variants in GATA4 and FOG2/ZFPM2 demonstrates benign contribution to 46,XY disorders of sex development

Background

GATA‐binding protein 4 (GATA4) and Friend of GATA 2 protein (FOG2, also known as ZFPM2) form a heterodimer complex that has been shown to influence transcription of genes in a number of developmental systems. Recent evidence has also shown these genes play a role in gonadal sexual differentiation in humans. Previously we identified four variants in GATA4 and an unexpectedly large number of variants in ZFPM2 in a cohort of individuals with 46,XY Differences/Disorders of Sex Development (DSD) (Eggers et al, Genome Biology, 2016; 17: 243).

Method

Here, we review variant curation and test the functional activity of GATA4 and ZFPM2 variants. We assess variant transcriptional activity on gonadal specific promoters (Sox9 and AMH) and variant protein–protein interactions.

Results

Our findings support that the majority of GATA4 and ZFPM2 variants we identified are benign in their contribution to 46,XY DSD. Indeed, only one variant, in the conserved N‐terminal zinc finger of GATA4, was considered pathogenic, with functional analysis confirming differences in its ability to regulate Sox9 and AMH and in protein interaction with ZFPM2.

Conclusions

Our study helps define the genetic factors contributing to 46,XY DSD and suggests that the majority of variants we identified in GATA4 and ZFPM2/FOG2 are not causative.

Congenital erythropoietic porphyria: Recent advances

Congenital erythropoietic porphyria (CEP) is a rare autosomal recessive disorder characterized by photosensitivity and by hematologic abnormalities in affected individuals. CEP is caused by mutations in the uroporphyrinogen synthase (UROS) gene. In three reported cases, CEP has been associated with a specific X-linked GATA1 mutation. Disease-causing mutations in either gene result in absent or markedly reduced UROS enzymatic activity. This in turn leads to the accumulation of the non-physiologic and photoreactive porphyrinogens, uroporphyrinogen I and coproporphyrinogen I, which damage erythrocytes and elicit a phototoxic reaction upon light exposure. The clinical spectrum of CEP depends on the level of residual UROS activity, which is determined by the underlying pathogenic loss-of-function UROS mutations. Disease severity ranges from non-immune hydrops fetalis in utero to late-onset disease with only mild cutaneous involvement. The clinical characteristics of CEP include exquisite photosensitivity to visible light resulting in bullous vesicular lesions which, when infected lead to progressive photomutilation of sun-exposed areas such as the face and hands. In addition, patients have erythrodontia (brownish discoloration of teeth) and can develop corneal scarring. Chronic transfusion-dependent hemolytic anemia is common and leads to bone marrow hyperplasia, which further increases porphyrin production. Management of CEP consists of strict avoidance of exposure to visible light with sun-protective clothing, sunglasses, and car and home window filters. Adequate care of ruptured vesicles and use of topical antibiotics is indicated to prevent superinfections and osteolysis. In patients with symptomatic hemolytic anemia, frequent erythrocyte cell transfusions may be necessary to suppress hematopoiesis and decrease marrow production of the phototoxic porphyrins. In severe transfection-dependent cases, bone marrow or hematopoietic stem cell transplantation has been performed, which is curative. Therapeutic approaches including gene therapy, proteasome inhibition, and pharmacologic chaperones are under investigation.

Origin and evolution of GATA2a and GATA2b in teleosts: insights from tongue sole, Cynoglossus semilaevis

Background. Following the two rounds of whole-genome duplication that occurred during deuterostome evolution, a third genome duplication occurred in the lineage of teleost fish and is considered to be responsible for much of the biological diversification within the lineage. GATA2, a member of GATA family of transcription factors, is an important regulator of gene expression in hematopoietic cell in mammals, yet the role of this gene or its putative paralogs in ray-finned fishes remains relatively unknown.

Methods. In this study, we attempted to identify GATA2 sequences from the transcriptomes and genomes of multiple teleosts using the bioinformatic tools MrBayes, MEME, and PAML. Following identification, comparative analysis of genome structure, molecular evolution rate, and expression by real-time qPCR were used to predict functional divergence of GATA2 paralogs and their relative transcription in organs of female and male tongue soles (Cynoglossus semilaevis).

Results. Two teleost GATA2 genes were identified in the transcriptomes of tongue sole and Japanese flounder (Paralichthysolivaceus). Synteny and phylogenetic analysis confirmed that the two genes likely originated from the teleost-specific genome duplication . Additionally, selection pressure analysis predicted these gene duplicates to have undergone purifying selection and possible divergent new functions. This was supported by differential expression pattern of GATA2a and GATA2b observed in organs of female and male tongue soles.

Discussion. Our results indicate that two GATA2 genes originating from the first teleost-specific genome duplication have remained transcriptionally active in some fish species and have likely undergone neofunctionalization. This knowledge provides novel insights into the evolution of the teleost GATA2 genes and constituted important groundwork for further research on the GATA gene family.

GATA3 mutations found in breast cancers may be associated with aberrant nuclear localization, reduced transactivation and cell invasiveness

Somatic and germline mutations in the dual zinc-finger transcription factor GATA3 are associated with breast cancers expressing the estrogen receptor (ER) and the autosomal dominant hypoparathyroidism-deafness-renal dysplasia syndrome, respectively. To elucidate the role of GATA3 in breast tumorigenesis, we investigated 40 breast cancers that expressed ER, for GATA3 mutations. Six different heterozygous GATA3 somatic mutations were identified in eight tumors, and these consisted of: a frameshifting deletion/insertion (944_945delGGinsAGC), an in-frame deletion of a key arginine residue (991_993delAGG), a seven-nucleotide frameshifting insertion (991_992insTGGAGGA), a frameshifting deletion (1196_1197delGA), and two frameshifting single nucleotide insertions (1224_1225insG found in three tumors and 1224_1225insA). Five of the eight mutations occurred in tumors that retained GATA3 immunostaining, indicating that absence of GATA3 immunostaining is an unreliable predictor of the presence of GATA3 mutations. Luciferase reporter assays, electrophoretic mobility shift assays, immunofluorescence, invasion and proliferation assays demonstrated that the GATA3 mutations resulted in loss (or reduction) of DNA binding, decrease in transactivational activity, and alterations in invasiveness but not proliferation. The 991_992insTGGAGGA (Arg330 frameshift) mutation led to a loss of nuclear localization, yet the 991_993delAGG (Arg330deletion) retained nuclear localization. Investigation of the putative nuclear localization signal (NLS) sites showed that the NLS of GATA3 does not conform to either a classical mono- or bi-partite signal, but contains multiple cooperative NLS elements residing around the N-terminal zinc-finger which comprises residues 264-288. Thus, approximately 20 % ER-positive breast cancers have somatic GATA3 mutations that lead to a loss of GATA3 transactivation activity and altered cell invasiveness.

Combinatorial regulation of tissue specification by GATA and FOG factors

The development of complex organisms requires the formation of diverse cell types from common stem and progenitor cells. GATA family transcriptional regulators and their dedicated co-factors, termed Friend of GATA (FOG) proteins, control cell fate and differentiation in multiple tissue types from Drosophila to man. FOGs can both facilitate and antagonize GATA factor transcriptional regulation depending on the factor, cell, and even the specific gene target. In this review, we highlight recent studies that have elucidated mechanisms by which FOGs regulate GATA factor function and discuss how these factors use these diverse modes of gene regulation to control cell lineage specification throughout metazoans.

Regulation of sperm gene expression by the GATA factor ELT-1

Cell fate specification is mediated primarily through the expression of cell-type-specific genes. The regulatory pathway that governs the sperm/egg decision in the hermaphrodite germ line of Caenorhabditis elegans has been well characterized, but the transcription factors that drive these developmental programs remain unknown. We report the identification of ELT-1, a GATA transcription factor that specifies hypodermal fate in the embryo, as a regulator of sperm-specific transcription in the germ line. Computational analysis identified a conserved bipartite sequence element that is found almost exclusively in the promoters of a number of sperm genes. ELT-1 was recovered in a yeast one-hybrid screen for factors that bind to that sperm consensus site. In vitro assays defined the sperm consensus sequence as an optimal binding site for ELT-1. We determined that expression of elt-1 is elevated in the sperm-producing germ line, and that ELT-1 is required for sperm function. Deletion of the ELT-1 binding site from a sperm promoter abrogates sperm-specific expression of a reporter transgene. This work demonstrates a role for the ELT-1 transcription factor in sperm, and provides a critical link between the germ line sex determination program and gamete-specific gene expression.

Crystal structures of multiple GATA zinc fingers bound to DNA reveal new insights into DNA recognition and self-association by GATA

The GATA family of transcription factors (GATA1-6) binds selected GATA sites in vertebrate genomes to regulate specific gene expression. Although vertebrate GATA factors have two highly conserved zinc finger motifs, how the two fingers act together to recognize functional DNA elements is not well understood. Here we determined the crystal structures of the C-terminal zinc finger of mouse GATA3 bound to DNA containing two variously arranged GATA binding sites. Our structures and accompanying biochemical analyses reveal two distinct modes of DNA binding by GATA to closely arranged sites. One mode involves cooperative binding by two GATA factors that interact with each other through protein-protein interactions. The other involves simultaneous binding of the N-terminal zinc finger (N-finger) and the C-terminal zinc finger of the same GATA factor. Our studies represent the first crystallographic analysis of GATA zinc fingers bound to DNA and provide new insights into the DNA recognition mechanism by the GATA zinc finger. Our crystal structure also reveals a dimerization interface in GATA that has previously been shown to be important for GATA self-association. These findings significantly advance our understanding of the structure and function of GATA and provide an important framework for further investigating the in vivo mechanisms of GATA-dependent gene regulation.

Point mutations in two EVI1 Zn fingers abolish EVI1-GATA1 interaction and allow erythroid differentiation of murine bone marrow cells

EVI1 is an aggressive nuclear oncoprotein deregulated by recurring chromosomal abnormalities in myelodysplastic syndrome (MDS). The expression of the corresponding gene is a very poor prognostic marker for MDS patients and is associated with severe defects of the erythroid lineage. We have recently shown that the constitutive expression of EVI1 in murine bone marrow results in a fatal disease with features characteristic of MDS, including anemia, dyserythropoiesis, and dysmegakaryopoiesis. These lineages are regulated by the DNA-binding transcription factor GATA1. EVI1 has two zinc finger domains containing seven motifs at the N terminus and three motifs at the C terminus. Supported by results of assays utilizing synthetic DNA promoters, it was earlier proposed that erythroid-lineage repression by EVI1 is based on the ability of this protein to compete with GATA1 for DNA-binding sites, resulting in repression of gene activation by GATA1. Here, however, we show that EVI1 is unable to bind to classic GATA1 sites. To understand the mechanism utilized by EVI1 to repress erythropoiesis, we used a combination of biochemical assays, mutation analyses, and in vitro bone marrow differentiation. The results indicate that EVI1 interacts directly with the GATA1 protein rather than the DNA sequence. We further show that this protein-protein interaction blocks efficient recognition or binding to DNA by GATA1. Point mutations that disrupt the geometry of two zinc fingers of EVI1 abolish the protein-protein interaction, leading to normal erythroid differentiation of normal murine bone marrow in vitro.

GATA1-mediated megakaryocyte differentiation and growth control can be uncoupled and mapped to different domains in GATA1

The DNA-binding hemopoietic zinc finger transcription factor GATA1 promotes terminal megakaryocyte differentiation and restrains abnormal immature megakaryocyte expansion. How GATA1 coordinates these fundamental processes is unclear. Previous studies of synthetic and naturally occurring mutant GATA1 molecules demonstrate that DNA-binding and interaction with the essential GATA1 cofactor FOG-1 (via the N-terminal finger) are required for gene expression in terminally differentiating megakaryocytes and for platelet production. Moreover, acquired mutations deleting the N-terminal 84 amino acids are specifically detected in megakaryocytic leukemia in human Down syndrome patients. In this study, we have systematically dissected GATA1 domains required for platelet release and control of megakaryocyte growth by ectopically expressing modified GATA1 molecules in primary GATA1-deficient fetal megakaryocyte progenitors. In addition to DNA binding, distinct N-terminal regions, including residues in the first 84 amino acids, promote platelet release and restrict megakaryocyte growth. In contrast, abrogation of GATA1-FOG-1 interaction leads to loss of differentiation, but growth of blocked immature megakaryocytes is controlled. Thus, distinct GATA1 domains regulate terminal megakaryocyte gene expression leading to platelet release and restrain megakaryocyte growth, and these processes can be uncoupled.

Ski negatively regulates erythroid differentiation through its interaction with GATA1

The Ski oncoprotein dramatically affects cell growth, differentiation, and/or survival. Recently, Ski was shown to act in distinct signaling pathways including those involving nuclear receptors, transforming growth factor beta, and tumor suppressors. These divergent roles of Ski are probably dependent on Ski's capacity to bind multiple partners with disparate functions. In particular, Ski alters the growth and differentiation program of erythroid progenitor cells, leading to malignant leukemia. However, the mechanism underlying this important effect has remained elusive. Here we show that Ski interacts with GATA1, a transcription factor essential in erythropoiesis. Using a Ski mutant deficient in GATA1 binding, we show that this Ski-GATA1 interaction is critical for Ski's ability to repress GATA1-mediated transcription and block erythroid differentiation. Furthermore, the repression of GATA1-mediated transcription involves Ski's ability to block DNA binding of GATA1. This finding is in marked contrast to those in previous reports on the mechanism of repression by Ski, which have described a model involving the recruitment of corepressors into DNA-bound transcription complexes. We propose that Ski cooperates in the process of transformation in erythroid cells by interfering with GATA1 function, thereby contributing to erythroleukemia.

GATA-1 and NF-Y cooperate to mediate erythroid-specific transcription of Gfi-1B gene

Expression of Gfi (growth factor-independence)-1B, a Gfi-1-related transcriptional repressor, is restricted to erythroid lineage cells and is essential for erythropoiesis. We have determined the transcription start site of the human Gfi-1B gene and located its first non-coding exon approximately 7.82 kb upstream of the first coding exon. The genomic sequence preceding this first non-coding exon has been identified to be its erythroid-specific promoter region in K562 cells. Using gel-shift and chromatin immunoprecipitation (ChIP) assays, we have demonstrated that NF-Y and GATA-1 directly participate in transcriptional activation of the Gfi-1B gene in K562 cells. Ectopic expression of GATA-1 markedly stimulates the activity of the Gfi-1B promoter in a non-erythroid cell line U937. Interestingly, our results have indicated that this GATA-1-mediated trans-activation is dependent on NF-Y binding to the CCAAT site. Here we conclude that functional cooperation between GATA-1 and NF-Y contributes to erythroid-specific transcriptional activation of Gfi-1B promoter.

Self-association of Gata1 enhances transcriptional activity in vivo in zebra fish embryos

Gata1 is a prototype transcription factor that regulates hematopoiesis, yet the molecular mechanisms by which Gata1 transactivates its target genes in vivo remain unclear. We previously showed, in transgenic zebra fish, that Gata1 autoregulates its own expression. In this study, we characterized the molecular mechanisms for this autoregulation by using mutations in the Gata1 protein which impair autoregulation. Of the tested mutations, replacement of six lysine residues with alanine (Gata1KA6), which inhibited self-association activity of Gata1, reduced the Gata1-dependent induction of reporter gene expression driven by the zebra fish gata1 hematopoietic regulatory domain (gata1 HRD). Furthermore, overexpression of wild-type Gata1 but not Gata1KA6 rescued the expression of Gata1 downstream genes in vlad tepes, a germ line gata1 mutant fish. Interestingly, both GATA sites in the double GATA motif in gata1 HRD were critical for the promoter activity and for binding of the self-associated Gata1 complex, whereas only the 3'-GATA site was required for Gata1 monomer binding. These results thus provide the first in vivo evidence that the ability of Gata1 to self-associate critically contributes to the autoregulation of the gata1 gene.

In vivo requirements for GATA-1 functional domains during primitive and definitive erythropoiesis

GATA-1 is a transcription factor essential for erythroid/megakaryocytic cell differentiation. To investigate the contribution of individual domains of GATA-1 to its activity, transgenic mice expressing either an N-terminus, or an N- or C-terminal zinc finger deletion of GATA-1 (Delta NT, Delta NF or Delta CF, respectively) were generated and crossed to GATA-1 germline mutant (GATA-1.05) mice. Since the GATA-1 gene is located on the X-chromosome, male GATA-1 mutants die by embryonic day 12.5. Both Delta NF and Delta CF transgenes failed to rescue the GATA-1.05/Y pups. However, transgenic mice expressing Delta NT, but not the Delta NF protein, were able to rescue definitive hematopoiesis. In embryos, while neither the Delta CF protein nor a mutant missing both N-terminal domains (Delta NTNF) was able to support primitive erythropoiesis, the two independent Delta NT and Delta NF mutants could support primitive erythropoiesis. Thus, lineage-specific transgenic rescue of the GATA-1 mutant mouse revealed novel properties that are conferred by specific domains of GATA-1 during primitive and definitive erythropoiesis, and demonstrate that the NT and NF moieties lend complementary, but distinguishable properties to the function of GATA-1.

Transcriptional repression and developmental functions of the atypical vertebrate GATA protein TRPS1

Known vertebrate GATA proteins contain two zinc fingers and are required in development, whereas invertebrates express a class of essential proteins containing one GATA-type zinc finger. We isolated the gene encoding TRPS1, a vertebrate protein with a single GATA-type zinc finger. TRPS1 is highly conserved between Xenopus and mammals, and the human gene is implicated in dominantly inherited tricho-rhino-phalangeal (TRP) syndromes. TRPS1 is a nuclear protein that binds GATA sequences but fails to transactivate a GATA-dependent reporter. Instead, TRPS1 potently and specifically represses transcriptional activation mediated by other GATA factors. Repression does not occur from competition for DNA binding and depends on a C-terminal region related to repressive domains found in Ikaros proteins. During mouse development, TRPS1 expression is prominent in sites showing pathology in TRP syndromes, which are thought to result from TRPS1 haploinsufficiency. We show instead that truncating mutations identified in patients encode dominant inhibitors of wild-type TRPS1 function, suggesting an alternative mechanism for the disease. TRPS1 is the first example of a GATA protein with intrinsic transcriptional repression activity and possibly a negative regulator of GATA-dependent processes in vertebrate development.

Mutational analysis of AREA, a transcriptional activator mediating nitrogen metabolite repression in Aspergillus nidulans and a member of the "streetwise" GATA family of transcription factors

The transcriptional activator AREA is a member of the GATA family of transcription factors and mediates nitrogen metabolite repression in the fungus Aspergillus nidulans. The nutritional versatility of A. nidulans and its amenability to classical and reverse genetic manipulations make the AREA DNA binding domain (DBD) a useful model for analyzing GATA family DBDs, particularly as structures of two AREA-DNA complexes have been determined. The 109 extant mutant forms of the AREA DBD surveyed here constitute one of the highest totals of eukaryotic transcription factor DBD mutants, are discussed in light of the roles of individual residues, and are compared to corresponding mutant sequence changes in other fungal GATA factor DBDs. Other topics include delineation of the DBD using both homology and mutational truncation, use of frameshift reversion to detect regions of tolerance to mutational change, the finding that duplication of the DBD can apparently enhance AREA function, and use of the AREA system to analyze a vertebrate GATA factor DBD. Some major points to emerge from work on the AREA DBD are (i) tolerance to sequence change (with retention of function) is surprisingly great, (ii) mutational changes in a transcription factor can have widely differing, even opposing, effects on expression of different structural genes so that monitoring expression of one or even several structural genes can be insufficient and possibly misleading, and (iii) a mutational change altering local hydrophobic packing and DNA binding target specificity can markedly influence the behavior of mutational changes elsewhere in the DBD.

GATA-4 and Nkx-2.5 coactivate Nkx-2 DNA binding targets: role for regulating early cardiac gene expression

The cardiogenic homeodomain factor Nkx-2.5 and serum response factor (SRF) provide strong transcriptional coactivation of the cardiac alpha-actin (alphaCA) promoter in fibroblasts (C. Y. Chen and R. J. Schwartz, Mol. Cell. Biol. 16:6372-6384, 1996). We demonstrate here that Nkx-2.5 also cooperates with GATA-4, a dual C-4 zinc finger transcription factor expressed in early cardiac progenitor cells, to activate the alphaCA promoter and a minimal promoter, containing only multimerized Nkx-2.5 DNA binding sites (NKEs), in heterologous CV-1 fibroblasts. Transcriptional activity requires the N-terminal activation domain of Nkx-2.5 and Nkx-2.5 binding activity through its homeodomain but does not require GATA-4's activation domain. The minimal interactive regions were mapped to the homeodomain of Nkx-2.5 and the second zinc finger of GATA-4. Removal of Nkx-2.5's C-terminal inhibitory domain stimulated robust transcriptional activity, comparable to the effects of GATA-4 on wild-type Nkx-2.5, which in part facilitated Nkx-2.5 DNA binding activity. We postulate the following simple model: GATA-4 induces a conformational change in Nkx-2.5 that displaces the C-terminal inhibitory domain, thus eliciting transcriptional activation of promoters containing Nkx-2.5 DNA binding targets. Therefore, alphaCa promoter activity appears to be regulated through the combinatorial interactions of at least three cardiac tissue-enriched transcription factors, Nkx-2.5, GATA-4, and SRF.

The cardiac tissue-restricted homeobox protein Csx/Nkx2.5 physically associates with the zinc finger protein GATA4 and cooperatively activates atrial natriuretic factor gene expression

Specification and differentiation of the cardiac muscle lineage appear to require a combinatorial network of many factors. The cardiac muscle-restricted homeobox protein Csx/Nkx2.5 (Csx) is expressed in the precardiac mesoderm as well as the embryonic and adult heart. Targeted disruption of Csx causes embryonic lethality due to abnormal heart morphogenesis. The zinc finger transcription factor GATA4 is also expressed in the heart and has been shown to be essential for heart tube formation. GATA4 is known to activate many cardiac tissue-restricted genes. In this study, we tested whether Csx and GATA4 physically associate and cooperatively activate transcription of a target gene. Coimmunoprecipitation experiments demonstrate that Csx and GATA4 associate intracellularly. Interestingly, in vitro protein-protein interaction studies indicate that helix III of the homeodomain of Csx is required to interact with GATA4 and that the carboxy-terminal zinc finger of GATA4 is necessary to associate with Csx. Both regions are known to directly contact the cognate DNA sequences. The promoter-enhancer region of the atrial natriuretic factor (ANF) contains several putative Csx binding sites and consensus GATA4 binding sites. Transient-transfection assays indicate that Csx can activate ANF reporter gene expression to the same extent that GATA4 does in a DNA binding site-dependent manner. Coexpression of Csx and GATA4 synergistically activates ANF reporter gene expression. Mutational analyses suggest that this synergy requires both factors to fully retain their transcriptional activities, including the cofactor binding activity. These results demonstrate the first example of homeoprotein and zinc finger protein interaction in vertebrates to cooperatively regulate target gene expression. Such synergistic interaction among tissue-restricted transcription factors may be an important mechanism to reinforce tissue-specific developmental pathways.

Distinct functions are implicated for the GATA-4, -5, and -6 transcription factors in the regulation of intestine epithelial cell differentiation

Based on conserved expression patterns, three members of the GATA family of transcriptional regulatory proteins, GATA-4, -5, and -6, are thought to be involved in the regulation of cardiogenesis and gut development. Functions for these factors are known in the heart, but relatively little is understood regarding their possible roles in the regulation of gut-specific gene expression. In this study, we analyze the expression and function of GATA-4, -5, and -6 using three separate but complementary vertebrate systems, and the results support a function for these proteins in regulating the terminal-differentiation program of intestinal epithelial cells. We show that xGATA-4, -5, and -6 can stimulate directly activity of the promoter for the intestinal fatty acid-binding protein (xIFABP) gene, which is a marker for differentiated enterocytes. This is the first direct demonstration of a target for GATA factors in the vertebrate intestinal epithelium. Transactivation by xGATA-4, -5, and -6 is mediated at least in part by a defined proximal IFABP promoter element. The expression patterns for cGATA-4, -5, and -6 are markedly distinct along the proximal-distal villus axis. Transcript levels for cGATA-4 increase along the axis toward the villus tip; likewise, cGATA-5 transcripts are largely restricted to the distal tip containing differentiated cells. In contrast, the pattern of cGATA-6 transcripts is complementary to cGATA-5, with highest levels detected in the region of proliferating progenitor cells. Undifferentiated and proliferating human HT-29 cells express hGATA-6 but not hGATA-4 or hGATA-5. Upon stimulation to differentiate, the transcript levels for hGATA-5 increase, and this occurs prior to increased transcription of the terminal differentiation marker intestinal alkaline phosphatase. At the same time, hGATA-6 steady-state transcript levels decline appreciably. All of the data are consistent with evolutionarily conserved but distinct roles for these factors in regulating the differentiation program of intestinal epithelium. Based on this data, we suggest that GATA-6 might function primarily within the proliferating progenitor population, while GATA-4 and GATA-5 function during differentiation to activate terminal-differentiation genes including IFABP.

Transcriptional activity of pannier is regulated negatively by heterodimerization of the GATA DNA-binding domain with a cofactor encoded by the u-shaped gene of Drosophila

The genes pannier (pnr) and u-shaped (ush) are required for the regulation of achaete-scute during establishment of the bristle pattern in Drosophila. pnr encodes a protein belonging to the GATA family of transcription factors, whereas ush encodes a novel zinc finger protein. Genetic interactions between dominant pnr mutants bearing lesions situated in the amino-terminal zinc finger of the GATA domain and ush mutants have been described. We show here that both wild-type Pannier and the dominant mutant form activate transcription from the heterologous alpha globin promoter when transfected into chicken embryonic fibroblasts. Furthermore, Pnr and Ush are found to heterodimerize through the amino-terminal zinc finger of Pnr and when associated with Ush, the transcriptional activity of Pnr is lost. In contrast, the mutant pnr protein with lesions in this finger associates only poorly with Ush and activates transcription even when cotransfected with Ush. These interactions have been investigated in vivo by overexpression of the mutant and wild-type proteins. The results suggest an antagonistic effect of Ush on Pnr function and reveal a new mode of regulation of GATA factors during development.

The second finger of Urbs1 is required for iron-mediated repression of sid1 in Ustilago maydis

The urbs1 gene encodes a transcriptional regulator of siderophore biosynthesis in Ustilago maydis. Biological and DNA-binding activities of the two putative zinc-finger motifs of Urbs1 were studied by analyzing mutants containing altered finger domains. The mutated urbs1 alleles from three previously described N'-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutants were mapped and cloned by a gap-repair procedure. Sequence analyses revealed single amino acid substitutions in two of the NTG mutants. Both mutations (G-507 to D in urbs1-1 and P-491 to L in urbs1-3), which are located in the Urbs1 C-terminal finger domain, reduced DNA-binding activity by 10-fold and were sufficient to confer a urbs1-minus phenotype. The third NTG urbs1 mutant (urbs1-2) also contained a mutation in one of the conserved amino acids (P-518 to S) in the C-terminal finger domain, but this mutation alone was not sufficient to confer a urbs1-minus phenotype. A second frame shift mutation was identified in urbs1-2 and is necessary for the urbs1-minus phenotype. In an analysis of the function of the N-terminal finger of Urbs1, the conserved amino acid Arg-350 was mutated to leucine. A Urbs1 protein with this mutation complemented a urbs1 null mutant strain. By contrast, a similar mutation in the C-terminal domain abolished the ability of Urbs1 to regulate siderophore biosynthesis and greatly reduced its ability to bind target DNA.

Genetic regulation of nitrogen metabolism in the fungi

In the fungi, nitrogen metabolism is controlled by a complex genetic regulatory circuit which ensures the preferential use of primary nitrogen sources and also confers the ability to use many different secondary nitrogen sources when appropriate. Most structural genes encoding nitrogen catabolic enzymes are subject to nitrogen catabolite repression, mediated by positive-acting transcription factors of the GATA family of proteins. However, certain GATA family members, such as the yeast DAL80 factor, act negatively to repress gene expression. Selective expression of the genes which encode enzymes for the metabolism of secondary nitrogen sources is often achieved by induction, mediated by pathway-specific factors, many of which have a GAL4-like C6/Zn2 DNA binding domain. Regulation within the nitrogen circuit also involves specific protein-protein interactions, as exemplified by the specific binding of the negative-acting NMR protein with the positive-acting NIT2 protein of Neurospora crassa. Nitrogen metabolic regulation appears to play a significant role in the pathogenicity of certain animal and plant fungal pathogens.

Erythroid-cell-specific properties of transcription factor GATA-1 revealed by phenotypic rescue of a gene-targeted cell line

The zinc finger transcription factor GATA-1 is essential for erythropoiesis. In its absence, committed erythroid precursors arrest at the proerythroblast stage of development and undergo apoptosis. To study the function of GATA-1 in an erythroid cell environment, we generated an erythroid cell line from in vitro-differentiated GATA-1- murine embryonic stem (ES) cells. These cells, termed G1E for GATA-1- erythroid, proliferate as immature erythroblasts yet complete differentiation upon restoration of GATA-1 function. We used rescue of terminal erythroid maturation in G1E cells as a stringent cellular assay system in which to evaluate the functional relevance of domains of GATA-1 previously characterized in nonhematopoietic cells. At least two major differences were established between domains required in G1E cells and those required in nonhematopoietic cells. First, an obligatory transactivation domain defined in conventional nonhematopoietic cell transfection assays is dispensable for terminal erythroid maturation. Second, the amino (N) zinc finger, which is nonessential for binding to the vast majority of GATA DNA motifs, is strictly required for GATA-1-mediated erythroid differentiation. Our data lead us to propose a model in which a nuclear cofactor(s) interacting with the N-finger facilitates transcriptional action by GATA-1 in erythroid cells. More generally, our experimental approach highlights critical differences in the action of cell-specific transcription proteins in different cellular environments and the power of cell lines derived from genetically modified ES cells to elucidate gene function.

Molecular dissection of a LIM domain

LIM domains are novel sequence elements that are found in more than 60 gene products, many of which function as key regulators of developmental pathways. The LIM domain, characterized by the cysteine-rich consensus CX2CX16-23HX2CX2CX2CX16-21 CX2-3(C/H/ D), is a specific mental-binding structure that consists of two distinct zinc-binding subdomains. We and others have recently demonstrated that the LIM domain mediates protein-protein interactions. However, the sequences that define the protein-binding specificity of the LIM domain had not yet been identified. Because structural studies have revealed that the C-terminal zinc-binding module of a LIM domain displays a tertiary fold compatible with nucleic acid binding, it was of interest to determine whether the specific protein-binding activity of a LIM domain could be ascribed to one of its two zinc-binding subdomains. To address this question, we have analyzed the protein-binding capacity of a model LIM peptide, called zLIM1, that is derived from the cytoskeletal protein zyxin. These studies demonstrate that the protein-binding function of zLIM1 can be mapped to sequences contained within its N-terminal zinc-binding module. The C-terminal zinc-binding module of zLIM1 may thus remain accessible to additional interactive partners. Our results raise the possibility that the two structural subdomains of a LIM domain are capable of performing distinct biochemical functions.

A palindromic regulatory site within vertebrate GATA-1 promoters requires both zinc fingers of the GATA-1 DNA-binding domain for high-affinity interaction

GATA-1, a transcription factor essential for the development of the erythroid lineage, contains two adjacent highly conserved zinc finger motifs. The carboxy-terminal finger is necessary and sufficient for specific binding to the consensus GATA recognition sequence: mutant proteins containing only the amino-terminal finger do not bind. Here we identify a DNA sequence (GATApal) for which the GATA-1 amino-terminal finger makes a critical contribution to the strength of binding. The site occurs in the GATA-1 gene promoters of chickens, mice, and humans but occurs very infrequently in other vertebrate genes known to be regulated by GATA proteins. GATApal is a palindromic site composed of one complete [(A/T)GATA(A/G)] and one partial (GAT) canonical motif. Deletion of the partial motif changes the site to a normal GATA site and also reduces by as much as eightfold the activity of the GATA-1 promoter in an erythroid precursor cell. We propose that GATApal is important for positive regulation of GATA-1 expression in erythroid cells.

The single Cys2-His2 zinc finger domain of the GAGA protein flanked by basic residues is sufficient for high-affinity specific DNA binding

Specific DNA binding to the core consensus site GAGAGAG has been shown with an 82-residue peptide (residues 310-391) taken from the Drosophila transcription factor GAGA. Using a series of deletion mutants, it was demonstrated that the minimal domain required for specific binding (residues 310-372) includes a single zinc finger of the Cys2-His2 family and a stretch of basic amino acids located on the N-terminal end of the zinc finger. In gel retardation assays, the specific binding seen with either the peptide or the whole protein is zinc dependent and corresponds to a dissociation constant of approximately 5 x 10(-9) M for the purified peptide. It has previously been thought that a single zinc finger of the Cys2-His2 family is incapable of specific, high-affinity binding to DNA. The combination of an N-terminal basic region with a single Cys2-His2 zinc finger in the GAGA protein can thus be viewed as a novel DNA binding domain. This raises the possibility that other proteins carrying only one Cys2-His2 finger are also capable of high-affinity specific binding to DNA.

Alternative translation initiation site usage results in two functionally distinct forms of the GATA-1 transcription factor

GATA-1 is a zinc-finger transcription factor that plays a critical role in the normal development of hematopoietic cell lineages. In human and murine erythroid cells a previously undescribed 40-kDa protein is detected with GATA-1-specific antibodies. We show that the 40-kDa GATA-1 (GATA-1s) is produced by the use of an internal AUG initiation codon in the GATA-1 transcript. The GATA-1 proteins share identical binding activity and form heterodimers in erythroleukemic cells but differ in their transactivation potential and in their expression in developing mouse embryos.

Regulation of Drosophila yolk protein genes by an ovary-specific GATA factor

The divergently transcribed yolk protein genes (Yp1 and Yp2) of Drosophila melanogaster are expressed only in adult females, in fat body tissue and in ovarian follicle cells. Using an in vitro transcription assay, we have identified a single 12-bp DNA element that activates transcription from the promoters of both Yp genes. In vivo, this regulatory element is tissue specific: it activates transcription of Yp1 and Yp2 reporter genes in follicle cells but has no detectable effect in fat body or other tissues. The sequence of the element consists of two recognition sites for the GATA family of transcription factors. We show that among the Drosophila genes known to encode GATA factors, only dGATAb is expressed in ovaries. The single transcript that we detect in ovaries is alternatively spliced or initiated to produce an ovary-specific isoform of the protein. Bacterially expressed dGATAb binds to the 12-bp element; a similar binding activity is also present in the Kc0 nuclear extracts used for in vitro transcription assays. These in vitro and in vivo results lead us to propose that dGATAb makes several developmentally regulated products, one of which is a follicle cell-specific protein activating transcription of Yp1 and Yp2 from a known regulatory element.

Isolation of a gene encoding a functional zinc finger protein homologous to erythroid Krüppel-like factor: identification of a new multigene family

We have identified and characterized the gene for a novel zinc finger transcription factor which we have termed lung Krüppel-like factor (LKLF). LKLF was isolated through the use of the zinc finger domain of erythroid Krüppel-like factor (ELKF) as a hybridization probe and is closely related to this erythroid cell-specific gene. LKLF is expressed in a limited number of tissues, with the predominant expression seen in the lungs and spleen. The gene is developmentally controlled, with expression noted in the 7-day embryo followed by a down-regulation at 11 days and subsequent reactivation. A high degree of similarity is noted in the zinc finger regions of LKLF and EKLF. Beyond this domain, the sequences diverge significantly, although the putative transactivation domains for both LKLF and EKLF are proline-rich regions. In the DNA-binding domain, the three zinc finger motifs are so closely conserved that the predicted DNA contact sites are identical, suggesting that both proteins may bind to the same core sequence. This was further suggested by transactivation assays in which mouse fibroblasts were transiently transfected with a human beta-globin reporter gene in the absence and presence of an LKLF cDNA construct. Expression of the LKLF gene activates this human beta-globin promoter containing the CACCC sequence previously shown to be a binding site for EKLF. Mutation of this potential binding site results in a significant reduction in the reporter gene expression. LKLF and EKLF can thus be grouped as members of a unique family of transcription factors which have discrete patterns of expression in different tissues and which appear to recognize the same DNA-binding site.

A novel DNA-binding domain that may form a single zinc finger motif

MNB1a is a DNA-binding protein from maize that interacts with the 35S promoter of cauliflower mosaic virus. This protein did not show significant homologies with any other DNA-binding protein and MNB1a seemed to be a member of a multigene family. In this study, isolation of cDNAs from the gene family to which MNB1a belongs revealed a unique conserved domain, referred to herein as the Dof domain, that contains a novel cysteine-rich motif for a single putative zinc finger. The amino acid sequence of the Dof domain and the arrangement of cysteine residues in this domain differ from those of known zinc finger motifs. However, the Dof domain was shown to be a DNA-binding domain that required Zn2+ ions for activity. Mutations at cysteine residues eliminated the DNA-binding activity of MNB1a. Thus, the Dof domain may be classified as a novel zinc finger motif. In addition, Southern blot analysis and a survey of DNA databases suggested that proteins that include Dof domains might exist in other eukaryotes, at least in the plant kingdom.

Functional synergy and physical interactions of the erythroid transcription factor GATA-1 with the Krüppel family proteins Sp1 and EKLF

An unresolved aspect of current understanding of erythroid cell-specific gene expression relates to how a limited number of transcriptional factors cooperate to direct high-level expression mediated by cis-regulatory elements separated over large distances within globin loci. In this report, we provide evidence that GATA-1, the major erythroid transcription factor, activates transcription in a synergistic fashion with two Krüppel family factors, the ubiquitous protein Sp1 and the erythroid-restricted factor EKLF (erythroid Krüppel-like factor), which recognize GC and/or GT/CACC motifs. Binding sites for both GATA-1 and these Krüppel proteins (especially Sp1) are found in close association in the promoters and enhancers of numerous erythroid cell-expressed genes and appear to cooperate in directing their expression. We have shown that GATA-1 interacts physically with Sp1 and EKLF and that interactions are mediated through their respective DNA-binding domains. Moreover, we show that GATA-1 and Sp1 synergize from a distance in constructs designed to mimic the architecture of globin locus control regions and downstream globin promoters. Finally, the formation of GATA-1-SP1 complexes was demonstrated in vivo by the ability of Sp1 to recruit GATA-1 to a promoter in the absence of GATA-binding sites. These experiments provide the first evidence for functionally important protein-protein interactions involved in erythroid cell-specific expression and suggest a mechanism by which DNA loops between locus control regions and globin promoters (or enhancers) might be formed or stabilized.

Self-association of the erythroid transcription factor GATA-1 mediated by its zinc finger domains

GATA-1, the founding member of a distinctive family of transcription factors, is expressed predominantly in erythroid cells and participates in the expression of numerous erythroid cell-expressed genes. GATA-binding sites are found in the promoters and enhancers of globin and nonglobin erythroid genes as well as in the alpha- and beta-globin locus control regions. To elucidate how GATA-1 may function in a variety of regulatory contexts, we have examined its protein-protein interactions. Here we show that GATA-1 self-associates in solution and in whole-cell extracts and that the zinc finger region of the molecule is sufficient to mediate this interaction. This physical interaction can influence transcription, as GATA-1 self-association is able to recruit a transcriptionally active but DNA-binding-defective derivative of GATA-1 to promoter-bound GATA-1 and result in superactivation. Through in vitro studies with bacterially expressed glutathione S-transferase fusion proteins, we have localized the minimal domain required for GATA-1 self-association to 40 amino acid residues within the C-terminal zinc finger region. Finally, we have detected physical interaction of GATA-1 with other GATA family members (GATA-2 and GATA-3) also mediated through the zinc finger domain. These findings have broad implications for the involvement of GATA factors in transcriptional control. In particular, the interaction of GATA-1 with itself and with other transcription factors may facilitate its function at diverse promoters in erythroid cells and also serve to bring together, or stabilize, loops between distant regulatory elements, such as the globin locus control regions and downstream globin promoters. We suggest that the zinc finger region of GATA-1, and related proteins, is multifunctional and mediates not only DNA binding but also important protein-protein interactions.

Homotypic interactions of chicken GATA-1 can mediate transcriptional activation

We used a one-hybrid system to replace precisely the finger II chicken GATA-1 DNA-binding domain with the binding domain of bacterial repressor protein LexA. The LexA DNA-binding domain lacks amino acids that function for transcriptional activation, nuclear localization, or protein dimerization. This allowed us to analyze activities of GATA-1 sequences distinct from DNA binding. We found that strong transcriptional activating sequences that function independently of finger II are present in GATA-1. Sequences including finger I contain an independent nuclear localizing function. Our data are consistent with cooperative binding of two LexA-GATA-1 hybrid proteins on a palindromic operator. The sensitivity of our transcription assay provides the first evidence that GATA-1 can make homotypic interactions in vivo. The ability of a non-DNA-binding form of GATA-1 to activate gene expression by targeting to a bound GATA-1 derivative further supports the notion that GATA-1-GATA-1 interactions may have functional consequences. A coimmunoprecipitation assay was used to demonstrate that GATA-1 multimeric complexes form in solution by protein-protein interaction. The novel ability of GATA-1 to interact homotypically may be important for the formation of higher-order structures among distant regulatory elements that share binding sites for this transcription factor. We also used the system to test the ability of GATA-1 to interact heterotypically with other activators.

Promoter control of translation in Xenopus oocytes

The HIV-1 promoter directs the high level production of transcripts in Xenopus oocytes. However, despite being exported to the cytoplasm, the transcripts are not translated [M. Braddock, A. M. Thorburn, A. Chambers, G. D. Elliott, G. J. Anderson, A. J. Kingsman and S. M. Kingsman (1990) Cell, 62, 1123-1133]. We have shown previously that this is a function of promoter sequences and is independent of the TAR RNA element that is normally located at the 5' end of all HIV mRNAs. We now show that a three nucleotide substitution at position -340, upstream of the RNA start site, reverses the translation inhibition. This site coincides with a sequence that can bind the haematopoietic transcription factor GATA. The inhibition of translation can also be reversed by treatment with inhibitors of casein kinase II or by injection into the nucleus of antibodies specific for the FRGY2 family of RNP proteins. We suggest that the -340 site influences the quality of the transcription complex such that transcripts are diverted to a nucleus-dependent translation inhibition pathway.

Rescue of GATA-1-deficient embryonic stem cells by heterologous GATA-binding proteins

Totipotent murine embryonic stem (ES) cells can be differentiated in vitro to form embryoid bodies (EBs) containing hematopoietic cells of multiple lineages, including erythroid cells. In vitro erythroid development parallels that which is observed in vivo. ES cells in which the gene for the erythroid transcription factor GATA-1 has been disrupted fail to produce mature erythroid cells either in vivo or in vitro. With the EB in vitro differentiation assay, constructs expressing heterologous GATA-binding proteins were tested for their abilities to correct the developmental defect of GATA-1-deficient ES cells. The results presented here show that the highly divergent chicken GATA-1 can rescue GATA-1 deficiency to an extent similar to that of murine GATA-1 (mGATA-1), as determined by size and morphology of EBs, presence of red cells, and globin gene expression. Furthermore, GATA-3 and GATA-4, which are normally expressed in different tissues, and a protein consisting of the zinc fingers of GATA-1 fused to the herpes simplex virus VP16 transcription activation domain were able to compensate for the GATA-1 defect. Chimeric molecules in which both zinc fingers of mGATA-1 were replaced with the zinc fingers of human GATA-3 or with the single finger of the fungal GATA factor areA, as well as a construct bearing the zinc finger region alone, displayed rescue activity. These results suggest that neither the transcription activation domains of mGATA-1 nor its zinc fingers impart erythroid cell specificity for its action in vivo. Rather, it appears that specificity is mediated through the cis-acting control regions which determine spatial and temporal expression of the GATA-1 gene. Furthermore, our results demonstrate that the zinc finger region may have a biological function in addition to mediating DNA binding.

The C-terminal zinc finger of GATA-1 or GATA-2 is sufficient to induce megakaryocytic differentiation of an early myeloid cell line

The GATA-1 and GATA-2 transcription factors, which each contain two homologous zinc fingers, are important hematopoietic regulators expressed within the erythroid, mast cell, and megakaryocytic lineages. Enforced expression of either factor in the primitive myeloid line 416B induces megakaryocytic differentiation. The features of their structure required for this activity have been explored. The ability of 12 GATA-1 mutants to promote 416B maturation was compared with their DNA-binding activity and transactivation potential. Differentiation did not require any of the seven serine residues that are phosphorylated in vivo, an N-terminal region bearing the major transactivation domain, or a C-terminal segment beyond the fingers. Removal of a consensus nuclear localization signal following the second finger did not block differentiation or nuclear translocation. The N-terminal finger was also dispensable, although its removal attenuated differentiation. In contrast, the C-terminal finger was essential, underscoring its distinct function. Remarkably, only 69 residues spanning the C-terminal finger were required to induce limited megakaryocytic differentiation. Analysis of three GATA-2 mutants led to the same conclusion. Endogenous GATA-1 mRNA was induced by most mutants and may contribute to differentiation. Because the GATA-1 C-terminal finger could bind its target site but not transactivate a minimal reporter, it may direct megakaryocytic maturation by derepressing specific genes and/or by interacting with another protein which provides the transactivation function.

Direct analysis of native and chimeric GATA specific DNA binding proteins from Aspergillus nidulans

In Aspergillus nidulans the regulatory gene areA is responsible for mediating nitrogen metabolite repression. The areA product (AREA) represents an example of the GATA family of DNA binding proteins, which are characterised by the presence of a GATA domain consisting of a zinc finger within a highly conserved region of 52 amino acids. Among the other transcription factors included in this family is the principal erythroid transcription factor, GATA-1, which contains two GATA domains. In order to demonstrate high specificity binding of native AREA to DNA containing the sequence -GATA-, and investigate the presence in A.nidulans of other proteins with related specificities, we have used gel mobility shift assays. Both AREA-dependent and independent complexes have been identified. Two strains bearing chimeric genes were also characterised. In these, the region encoding the native GATA domain of AREA was replaced by sequences from murine GATA-1 cDNA encoding either the equivalent C-terminal domain or both the N and C-terminal domains. Strains bearing the areA::NC-GATA construct, which includes the sequence encoding both the N and C-terminal domains of GATA-1, leads to a pronounced increase in one of two AREA-dependent complexes and implicates the N-terminal domain of GATA-1 in mediating protein-protein interactions.

Structure, expression and gene sequence of a juvenile hormone esterase-related protein from metamorphosing larvae of Trichoplusia ni

A carboxylesterase with an encoded molecular size of 61 kDa and a high sequence similarity to juvenile hormone esterase (JHE) has been cloned from cDNA prepared from final instar larvae of Trichoplusia ni. The absence of a recognizable encoded signal peptide suggests that the enzyme, JHER (for JHE-related) may not be secreted, in contrast to JHE. When the amino acid sequence of JHE, JHER and other esterases were mapped onto the secondary and tertiary structure determined crystallographically for acetylcholinesterase, certain structural features for the substrate binding/catalytic site were identified as common only to JHE and JHER. However, several differences between JHE and JHER were identified in residues at the binding/catalytic site, suggesting that although the two enzymes prefer similar natural substrates, these substrates are not identical. JHER is present as a single-copy gene, transcribed during the feeding stage of the final stage of the final larval stadium, but not after metamorphic commitment to the pupal developmental programme. The gene transcribes a single-size message of 2.0 kb. The genes for JHER and JHE appear to be physically juxtaposed in the T. ni genome. The 5' flanking sequence to the JHER gene possesses some sequences in common with the JHE gene, but is also missing some regulatory elements previously identified in the JHE gene. Sequences conserved between the promoters for the two genes were identified that were different from previously reported regulatory elements of eukaryotic transcription factors.

The UGA4 UASNTR site required for GLN3-dependent transcriptional activation also mediates DAL80-responsive regulation and DAL80 protein binding in Saccharomyces cerevisiae

Expression of the nitrogen catabolic genes in Saccharomyces cerevisiae, including those of the gamma-aminobutyric acid (UGA) and allantoin (DAL) pathways, is regulated positively by the GLN3 protein and negatively by the DAL80 protein. The deduced sequences of the DAL80 and GLN3 proteins contain a zinc finger motif homologous to those shown to bind GATA sequences. In addition, DAL80 protein has been directly shown to bind to a pair of GATA-containing sequences (URSGATA) in vitro, and a pair of GATA-containing sequences (UASNTR) is required for GLN3-dependent transcriptional activation in a heterologous expression vector. We demonstrate here that the GATA-containing sites upstream of UGA4 required for optimal GLN3-dependent transcriptional activation also mediate DAL80 protein binding in vitro and DAL80-responsive regulation in vivo.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.

Human GATA-3 trans-activation, DNA-binding, and nuclear localization activities are organized into distinct structural domains

GATA-3 is a zinc finger transcription factor which is expressed in a highly restricted and strongly conserved tissue distribution pattern in vertebrate organisms, specifically, in a subset of hematopoietic cells, in cells within the central and peripheral nervous systems, in the kidney, and in placental trophoblasts. Tissue-specific cellular genes regulated by GATA-3 have been identified in T lymphocytes and the placenta, while GATA-3-regulated genes in the nervous system and kidney have not yet been defined. We prepared monoclonal antibodies with which we could dissect the biochemical and functional properties of human GATA-3. The results of these experiments show some anticipated phenotypes, for example, the definition of discrete domains required for specific DNA-binding site recognition (amino acids 303 to 348) and trans activation (amino acids 30 to 74). The signaling sequence for nuclear localization of human GATA-3 is a property conferred by sequences within and surrounding the amino finger (amino acids 249 to 311) of the protein, thereby assigning a function to this domain and thus explaining the curious observation that this zinc finger is dispensable for DNA binding by the GATA family of transcription factors.

Human GATA-3 trans-activation, DNA-binding, and nuclear localization activities are organized into distinct structural domains

GATA-3 is a zinc finger transcription factor which is expressed in a highly restricted and strongly conserved tissue distribution pattern in vertebrate organisms, specifically, in a subset of hematopoietic cells, in cells within the central and peripheral nervous systems, in the kidney, and in placental trophoblasts. Tissue-specific cellular genes regulated by GATA-3 have been identified in T lymphocytes and the placenta, while GATA-3-regulated genes in the nervous system and kidney have not yet been defined. We prepared monoclonal antibodies with which we could dissect the biochemical and functional properties of human GATA-3. The results of these experiments show some anticipated phenotypes, for example, the definition of discrete domains required for specific DNA-binding site recognition (amino acids 303 to 348) and trans activation (amino acids 30 to 74). The signaling sequence for nuclear localization of human GATA-3 is a property conferred by sequences within and surrounding the amino finger (amino acids 249 to 311) of the protein, thereby assigning a function to this domain and thus explaining the curious observation that this zinc finger is dispensable for DNA binding by the GATA family of transcription factors.

The Saccharomyces cerevisiae DAL80 repressor protein binds to multiple copies of GATAA-containing sequences (URSGATA)

Induced expression of the allantoin (DAL) catabolic genes in Saccharomyces cerevisiae has been suggested to be mediated by interaction of three different types of promoter elements. First is an inducer-independent upstream activation sequence, UASNTR, whose operation is sensitive to nitrogen catabolite repression. The GLN3 product is required for UASNTR-mediated transcriptional activation. This site consists of two separated elements, each of which has a GATAA sequence at its core. Response of the DAL genes to inducer is mediated by a second type of cis-acting element, DAL UIS. The DAL82 and DAL81 genes are required for response to inducer; DAL82 protein is the UIS-binding protein. When only the UASNTR and UIS elements are present, DAL gene expression occurs at high levels in the absence of inducer. We, therefore, hypothesized that a third element, an upstream repressor sequence (URS) mediates maintenance of DAL gene expression at a low level when inducer is absent. Since the DAL and UGA genes are overexpressed and largely inducer independent in dal80 deletion mutants, we have suggested DAL80 protein negatively regulates a wide spectrum of nitrogen-catabolic gene expression, likely in conjunction with a URS element. Here we show that DAL80 protein binds to DAL3 and UGA4 upstream DNA sequences, designated URSGATA, consisting of two GATAA-containing sites separated by at least 15 bp. The preferred orientation of the sites is tail to tail, but reasonable binding activity is also observed with a head-to-tail configuration. URSGATA elements contain the sequence GATAA at their core and hence share sequence homology with UASNTR elements.

DNA-binding specificities of the GATA transcription factor family

Members of the GATA family of transcription factors, which are related by a high degree of amino acid sequence identity within their zinc finger DNA-binding domains, each show distinct but overlapping patterns of tissue-restricted expression. Although GATA-1, -2, and -3 have been shown to recognize a consensus sequence derived from regulatory elements in erythroid cell-specific genes, WGATAR (in which W indicates A/T and R indicates A/G), the potential for more subtle differences in the binding preferences of each factor has not been previously addressed. By employing a binding selection and polymerase chain reaction amplification scheme with randomized oligonucleotides, we have determined the binding-site specificities of bacterially expressed chicken GATA-1, -2, and -3 transcription factors. Whereas all three GATA factors bind an AGATAA erythroid consensus motif with high affinity, a second, alternative consensus DNA sequence, AGATCTTA, is also recognized well by GATA-2 and GATA-3 but only poorly by GATA-1. These studies suggest that all three GATA factors are capable of mediating transcriptional effects via a common erythroid consensus DNA-binding motif. Furthermore, GATA-2 and GATA-3, because of their distinct expression patterns and broader DNA recognition properties, may be involved in additional regulatory processes beyond those of GATA-1. The definition of an alternative GATA-2-GATA-3 consensus sequence may facilitate the identification of new target genes in the further elucidation of the roles that these transcription factors play during development.

DNA-binding specificity of GATA family transcription factors

GATA-binding proteins constitute a family of transcription factors that recognize a target site conforming to the consensus WGATAR (W = A or T and R = A or G). Here we have used the method of polymerase chain reaction-mediated random site selection to assess in an unbiased manner the DNA-binding specificity of GATA proteins. Contrary to our expectations, we show that GATA proteins bind a variety of motifs that deviate from the previously assigned consensus. Many of the nonconsensus sequences bind protein with high affinity, equivalent to that of conventional GATA motifs. By using the selected sequences as probes in the electrophoretic mobility shift assay, we demonstrate overlapping, but distinct, sequence preferences for GATA family members, specified by their respective DNA-binding domains. Furthermore, we provide additional evidence for interaction of amino and carboxy fingers of GATA-1 in defining its binding site. By performing cotransfection experiments, we also show that transactivation parallels DNA binding. A chimeric protein containing the finger domain of areA and the activation domains of GATA-1 is capable of activating transcription in mammalian cells through GATA motifs. Our findings suggest a mechanism by which GATA proteins might selectively regulate gene expression in cells in which they are coexpressed.