DNA sequences required for regulated expression of beta-globin genes in murine erythroleukemia cells

A novel in vivo transcription assay demonstrates the presence of globin-inducing trans-acting factors in uninduced murine erythroleukemia cells

We report the development of a novel in vivo transcription assay for trans-acting factors regulating the human gamma- and beta-globin genes. A cDNA coding for the human tissue-type plasminogen activator (t-PA) was inserted into the globin genes. Simian virus 40 small T-antigen splice and polyadenylation signals were included to produce a mature transcript coding for t-PA, whose activity can be detected in single cells by a fibrin-agarose plaque assay. Stable murine L-cell transfectants of the gamma.t-PA and beta.t-PA hybrid genes were fused to various cell lines to show that t-PA expression is increased specifically by erythroid MEL, HEL, and K562 cell fusion. The analogous H-2Kb.t-PA construct was not inducible under the same conditions. Interestingly, uninduced MEL cells increased beta.t-PA expression to the same extent as induced MEL cells. Chemiosmotic permeabilization of the beta-globin tester cell line and exposure to nuclear extracts were used to assay for trans-acting factors capable of stimulating beta.t-PA expression. Such factors were shown to be present in the nuclei of uninduced MEL cells.

Detection of two tissue-specific DNA-binding proteins with affinity for sites in the mouse beta-globin intervening sequence 2

To identify proteins from uninduced murine erythroleukemia nuclear extracts which specifically bind to sequences from the DNase I-hypersensitive region within the mouse beta-globin intervening sequence 2 (IVS2), a gel electrophoretic mobility shift assay was used. Two distinct sequence-specific binding proteins were detected. The specific binding sites for these factors were delineated by both DNase I protection footprinting and methylation interference. Factor B1 bound specifically to two homologous sites, B1-A and B1-B, approximately 100 base pairs apart within the IVS2 and on opposite strands. These two regions could interact with factor B1 independently. Factor B1 was limited to cells of hematopoietic lineages. Factor B2 bound to a site approximately 5 base pairs away from the B1-A site and was limited to cells of the erythroid lineage. The limited tissue distribution of these factors and the locations of their binding sites suggest that one or both of these factors may be involved in the formation of the tissue-specific DNase I-hypersensitive site in the IVS2 of the mouse beta-globin gene.

Differential requirements for cellular enhancers in stem and differentiated cells

Multiple cis-acting regulatory elements consisting of three cellular enhancers and a proximal promoter element have been identified in the region upstream of the mouse alpha-fetoprotein (AFP) gene. We examined the role of these sequences during differentiation by the introduction of modified AFP genes into cells at different stages of commitment to its expression. Modified AFP genes introduced stably into F9 embryonal carcinoma stem cells by DNA transfection were silent until activated by treatment with retinoic acid to form visceral endoderm. Their activation required the presence of both the enhancer and proximal promoter domains. The introduced genes activated simultaneously with the endogenous AFP genes, but reached maximal levels of expression more rapidly, suggesting a greater initial accessibility to transcription factors. In contrast, when modified AFP genes were stably introduced into HepG2 cells, a human hepatoma cell line that constitutively expresses the AFP gene, the proximal promoter sequences were sufficient to direct a low level of expression. The absolute requirement for the AFP enhancers in F9 cells but not in HepG2 cells supports a model by which there is an obligate requirement for enhancers during differentiation in addition to their role in enhancing gene expression after differentiation.

RNA processing of beta-globin transcripts containing 5' flanking and structural gene sequences

RNA species have been identified in murine erythroid cells which contain both 5' flanking and structural gene sequences from the beta maj globin gene. Two nonpolyadenylated RNA transcripts, average 3700 and 1800-1900 nucleotides long, were identified by denaturing agarose gel electrophoresis and were found to hybridize to both 5' and 3' beta maj globin flanking sequences. This finding suggests that transcription initiated in the 5' flanking region does proceed past the polyadenylation site. The apparent higher concentration of the 5' flanking sequences in precursor RNA molecules, as compared to mature polyadenylated globin mRNA, suggests increased precursor stability of beta globin transcripts initiated in the 5' flanking region.

A novel in vivo transcription assay demonstrates the presence of globin-inducing trans-acting factors in uninduced murine erythroleukemia cells

We report the development of a novel in vivo transcription assay for trans-acting factors regulating the human gamma- and beta-globin genes. A cDNA coding for the human tissue-type plasminogen activator (t-PA) was inserted into the globin genes. Simian virus 40 small T-antigen splice and polyadenylation signals were included to produce a mature transcript coding for t-PA, whose activity can be detected in single cells by a fibrin-agarose plaque assay. Stable murine L-cell transfectants of the gamma.t-PA and beta.t-PA hybrid genes were fused to various cell lines to show that t-PA expression is increased specifically by erythroid MEL, HEL, and K562 cell fusion. The analogous H-2Kb.t-PA construct was not inducible under the same conditions. Interestingly, uninduced MEL cells increased beta.t-PA expression to the same extent as induced MEL cells. Chemiosmotic permeabilization of the beta-globin tester cell line and exposure to nuclear extracts were used to assay for trans-acting factors capable of stimulating beta.t-PA expression. Such factors were shown to be present in the nuclei of uninduced MEL cells.

Detection of two tissue-specific DNA-binding proteins with affinity for sites in the mouse beta-globin intervening sequence 2

To identify proteins from uninduced murine erythroleukemia nuclear extracts which specifically bind to sequences from the DNase I-hypersensitive region within the mouse beta-globin intervening sequence 2 (IVS2), a gel electrophoretic mobility shift assay was used. Two distinct sequence-specific binding proteins were detected. The specific binding sites for these factors were delineated by both DNase I protection footprinting and methylation interference. Factor B1 bound specifically to two homologous sites, B1-A and B1-B, approximately 100 base pairs apart within the IVS2 and on opposite strands. These two regions could interact with factor B1 independently. Factor B1 was limited to cells of hematopoietic lineages. Factor B2 bound to a site approximately 5 base pairs away from the B1-A site and was limited to cells of the erythroid lineage. The limited tissue distribution of these factors and the locations of their binding sites suggest that one or both of these factors may be involved in the formation of the tissue-specific DNase I-hypersensitive site in the IVS2 of the mouse beta-globin gene.

The interplay of DNA-binding proteins on the promoter of the mouse albumin gene

The promoter of the mouse albumin gene contains at least six binding sites for specific DNA-binding proteins (A to F). Four of these sites (A, D, E, and F) can be occupied by transcription factors that are considerably enriched in liver nuclei, as compared to spleen or brain nuclei. These factors consist of a heat-stable protein that fills sites A, D, and F, and a member of a family of nuclear factor I (NF-I) related proteins that occupies site E. Site C binds a protein that is equally abundant in liver, brain, and spleen nuclei. Occupancy of this site and the binding of the heat-stable factor to the immediately adjacent site D appear to be mutually exclusive. However, both of these competing binding sites are required for maximal in vitro transcription.

Position-independent, high-level expression of the human beta-globin gene in transgenic mice

We have constructed a "minilocus" that contains the 5' and 3' flanking regions of the human beta-globin locus and the beta-globin gene. These regions are characterized by erythroid-specific DNAase I-superhypersensitive sites and are normally located approximately 50 kb 5' and 20 kb 3' of the beta-globin gene. This minilocus is expressed tissue-specifically in transgenic mice at a level directly related to its copy number yet independent of its position of integration in the genome. Moreover, the expression per gene copy is the same in each mouse and as high as that of the endogenous mouse beta-globin gene. These results indicate that the DNA regions flanking the human beta-globin locus contain dominant regulatory sequences that specify position-independent expression and normally activate the complete human multigene beta-globin locus.

Evidence for a locus activation region: the formation of developmentally stable hypersensitive sites in globin-expressing hybrids

We have analyzed the chromatin structure of the human beta-globin locus in somatic cell hybrids resulting from the fusion of human non-erythroid cells and mouse erythroleukemia (MEL) cells. In these hybrids, the human adult beta-globin gene, but neither the embryonic nor fetal globin genes, is activated transcriptionally. In addition, the DNase I-resistant beta-like globin locus characteristic of the parental non-erythroid human cells (1,2) is reorganized over an approximately 80 kb region, including the formation of the developmentally stable hypersensitive sites 50 kb 5' and 20 kg 3' of the activated adult beta-globin gene (2,3). These results are consistent with the hypothesis that events occurring at the 5' and/or 3' developmentally stable hypersensitive sites are important, if not necessary, for the activation of the beta-globin locus.

Expression of the affected A gamma globin gene associated with Greek nondeletion hereditary persistence of fetal hemoglobin

The overexpressed A gamma globin gene in the Greek type of nondeletion hereditary persistence of fetal hemoglobin has a unique single-base substitution located at position -117 relative to the site of transcription initiation. This gene and its normal counterpart were transferred into cultured cell lines by using a retroviral vector. The only difference in expression between the transferred normal and mutant gamma genes was observed in the human erythroleukemia cell line KMOE after exposure of the cells to cytosine arabinoside, a condition that resulted in an adult pattern of endogenous globin gene expression by the cells and was associated with increased expression of the mutant gene.

Induction of transformed cells to terminal differentiation

HMBA induces MEL cells to terminal erythroid differentiation. HMBA causes a decrease in diacylglycerol concentration, a decrease in Ca+2 and phospholipid-dependent protein kinase C activity (within 2 hr). There is an early (within 1-2 hrs) suppression of c-myb and c-myc gene transcription and an increase in c-fos mRNA (within 4 hrs). During the early or "latent" period there is no detectable commitment of MELC to terminal cell division or expression of differentiated genes such as alpha 1 or beta maj globin genes. HMBA-induced commitment to terminal differentiation is detected by 12 hrs and over 95% become committed cells by 48-60 hrs. Commitment is associated with persistent suppression of c-myb gene transcription and elevated levels of c-fos mRNA, whereas the level of c-myc mRNA returns to that of uninduced cells. By 36-48 hrs, transcription of the alpha 1 and beta maj globin genes increases 10-30 fold, and that of rRNA genes is suppressed. Changes in expression of c-myb, c-myc, c-fos and p53 genes that occur early during HMBA-induced differentiation may be important in the multistep process involved in commitment of MEL cells to terminal differentiation. Continued suppression of c-myb gene expression may be required for terminal differentiation of these cells.

Human beta-globin gene expression after gene transfer using retroviral vectors

A retroviral vector containing a 4.4-kb Pst I human beta S-globin gene and a neomycin resistance gene was used to infect NIH-3T3 and mouse erythroleukemia cells (MELC). In MELC, human beta-globin mRNA transcripts are transcribed and properly initiated and spliced. In some cases, there is an appropriate increase in beta-globin mRNA on addition of dimethylsulfoxide (DMSO), an inducer of hemoglobin synthesis and erythroid differentiation in these cells. When NIH-3T3 cells are infected with the same retroviral vector, there is less globin mRNA accumulation and no evidence for appropriate regulation. Human beta-globin gene expression in MELC clones induced with DMSO is 2-3% that of endogenous mouse beta-globin gene expression. These results indicate that retroviral vectors can be used to transfer and appropriately express human beta-globin genes in erythroid cells.

Regulation of adult and embryonic genes in human leukemia cells

In this article, we have reviewed studies showing that altered expression of regulatory genes results in activation of embryonic genes in human leukemia cells. These data have led to important new insights as to how mutations in regulatory genes can lead to disease states in man.

Upstream G gamma-globin and downstream beta-globin sequences required for stage-specific expression in transgenic mice

The human G gamma-globin and beta-globin genes are expressed in erythroid cells at different stages of human development, and previous studies have shown that the two cloned genes are also expressed in a differential stage-specific manner in transgenic mice. The G gamma-globin gene is expressed only in murine embryonic erythroid cells, while the beta-globin gene is active only at the fetal and adult stages. In this study, we analyzed transgenic mice carrying a series of hybrid genes in which different upstream, intragenic, or downstream sequences were contributed by the beta-globin or G gamma-globin gene. We found that hybrid 5'G gamma/3'beta globin genes containing G gamma-globin sequences upstream from the initiation codon were expressed in embryonic erythroid cells at levels similar to those of an intact G gamma-globin transgene. In contrast, beta-globin upstream sequences were insufficient for expression of 5'beta/3'G gamma hybrid globin genes or a beta-globin-metallothionein fusion gene in adult erythroid cells. However, beta-globin downstream sequences, including 212 base pairs of exon III and 1,900 base pairs of 3'-flanking DNA, were able to activate a 5'G gamma/3'beta hybrid globin gene in fetal and adult erythroid cells. These experiments suggest that positive regulatory elements upstream from the G gamma-globin and downstream from the beta-globin gene are involved in the differential expression of the two genes during development.

Expression of transfected vimentin genes in differentiating murine erythroleukemia cells reveals divergent cis-acting regulation of avian and mammalian vimentin sequences

We studied the expression of transfected chicken and hamster vimentin genes in murine erythroleukemia (MEL) cells. MEL cells normally repress the levels of endogenous mouse vimentin mRNA during inducermediated differentiation, resulting in a subsequent loss of vimentin filaments. Expression of vimentin in differentiating MEL cells reflects the disappearance of vimentin filaments during mammalian erythropoiesis in vivo. In contrast, chicken erythroid cells express high levels of vimentin mRNA and vimentin filaments during terminal differentiation. We demonstrate here that chicken vimentin mRNA levels increase significantly in differentiating transfected MEL cells, whereas similarly transfected hamster vimentin genes are negatively regulated. In conjunction with in vitro nuclear run-on transcription experiments, these results suggest that the difference in vimentin expression in avian and mammalian erythropoiesis is due to a divergence of cis-linked vimentin sequences that are responsible for transcriptional and posttranscriptional regulation of vimentin gene expression. Transfected chicken vimentin genes produce functional vimentin protein and stable vimentin filaments during MEL cell differentiation, further demonstrating that the accumulation of vimentin filaments is determined by the abundance of newly synthesized vimentin.

Promoter efficiency depends upon intragenic sequences

Experiments concerning gene transcription in Xenopus oocytes have revealed that the efficiency of the HSV-TK promoter is dependent upon the nature of the attached gene sequences. Transcriptional efficiency of the TK promoter when attached to its own gene was 30-fold higher than that observed when the promoter was attached either to an avian keratin gene or to the chicken histone H2B gene. Furthermore, attachment of the keratin gene promoter to the TK gene resulted in a 20-fold increase in keratin promoter efficiency. It was found by subsequent experiments that the TK gene is able to exert a stimulatory influence upon attached promoter sequences. This cis effect was shown to be independent of orientation but dependent upon the distance between the DNA sequences involved.

A transcriptional activator is located in the coding region of the yeast PGK gene

Expression of heterologous genes from the PGK promoter on high copy number plasmids in yeast is relatively poor compared to the intact PGK gene because of low steady-state RNA levels. In this paper we show that low levels of heterologous RNA are not due to instability of mRNA but result from inefficient transcription due to a defect in RNA synthesis. A comparison of RNA levels from homologous and heterologous transcription units allowed the identification of a positive activator for transcription within the PGK coding region which is required for efficient expression of the PGK gene. Deletion of this region, the "downstream activator sequence", causes a six to ten fold reduction in transcriptional efficiency from the PGK 5' noncoding region.

Expression of the affected A gamma globin gene associated with Greek nondeletion hereditary persistence of fetal hemoglobin

The overexpressed A gamma globin gene in the Greek type of nondeletion hereditary persistence of fetal hemoglobin has a unique single-base substitution located at position -117 relative to the site of transcription initiation. This gene and its normal counterpart were transferred into cultured cell lines by using a retroviral vector. The only difference in expression between the transferred normal and mutant gamma genes was observed in the human erythroleukemia cell line KMOE after exposure of the cells to cytosine arabinoside, a condition that resulted in an adult pattern of endogenous globin gene expression by the cells and was associated with increased expression of the mutant gene.

Activation of the human beta-globin promoter in K562 cells by DNA sequences 5' to the fetal gamma- or embryonic zeta-globin genes

Regulatory sequences of the human fetal gamma-globin gene were studied by constructing composite gamma/beta globin promoters and comparing their function to that of intact beta promoters in human K562 cells. The beta-globin gene with either 1,600 or 127 basepairs of beta promoter sequence was not expressed after stable introduction into K562 cells, consistent with the known inactivity of the beta-globin gene in these cells. In contrast, a gamma/beta promoter composed of a gamma fragment spanning positions -408 to -137 joined to the 127-bp beta promoter was able to drive the beta-globin gene. The gene appeared to be inducible with hemin. A zeta-globin 5' flanking fragment also activated the beta promoter. The function of a series of composite gamma/beta promoters was then assessed by their ability to drive directly the neomycin resistance gene, again in stably transformed cells. The -408 to -137 gamma fragment activated the beta promoter in an orientation-specific manner in this assay. Deletion analysis showed that regulatory sequences were present between positions -259 and -137 of the fetal gamma-globin gene flanking region.

The human beta-globin gene contains a downstream developmental specific enhancer

The human beta-globin gene is part of a multigene family and is expressed specifically in adult human erythroid tissue (for review, 1). When the human beta-globin is introduced into fertilized mouse eggs, it is first activated in foetal liver and remains expressed in adult erythroid tissues. It therefore mimicks the pattern of expression of its murine counterpart. It has previously been shown in tissue culture and transgenic mice that sequences downstream from the beta-globin promoter are involved in this regulation. We now show that at least part of these sequences are located 0.5-1.2kb downstream from the poly A addition site and constitute a transcriptional enhancer element that is erythroid and developmental specific.

A pituitary-specific trans-acting factor can stimulate transcription from the growth hormone promoter in extracts of nonexpressing cells

The growth hormone (GH) gene is specifically expressed in the anterior pituitary. The first 289 bp of the human (h)GH 5' region contains a promoter that is active only in pituitary-derived cell lines. These cell lines also contain a specific factor, GHF-1, that binds to two sites upstream to the hGH TATA box. Using in vitro transcription systems we demonstrate greater hGH promoter activity in extracts of GH-expressing GC cells than in extracts of nonexpressing HeLa cells. The two GHF-1 binding sites are essential promoter elements in GC extracts. Addition of GHF-1-containing fractions to HeLa extracts stimulates hGH promoter activity. Thus, GHF-1 appears to be a positively acting, cell-type- and promoter-specific transcription factor. Furthermore, the tissue specificity of the hGH promoter appears to be positively controlled by the abundance or activity of GHF-1.

Cooperative interaction of multiple DNA elements in the human interferon-beta promoter

Analysis of promoter mutants and hybrids in permanently transformed murine L cells reveals several regulatory DNA sequence elements in the 5' flanking region of the human interferon-beta gene, which together constitute the inducible promoter. The elements consist almost exclusively of purine runs in the region -111 to -1. Deletion of single elements reduces the expression capacity drastically, whereas duplication leads to a synergism of inducible expression. These elements act together in a cooperative way to achieve high inducibility. Natural and mutant promoter fragments containing these elements impose inducibility on a heterologous promoter. However, typical enhancer activity in this system is not observed.

B-lymphoma induction by reticuloendotheliosis virus: characterization of a mutated chicken syncytial virus provirus involved in c-myc activation

Nondefective reticuloendotheliosis virus induces chicken bursal lymphoma in a manner similar to that of avian leukosis virus. The provirus integrates in the c-myc locus and uses a promoter insertion mechanism to activate c-myc expression. We cloned a provirus involved in c-myc activation from a B lymphoma. Detailed structural characterization of this clone, including sequence determination, revealed proviral insertion at 512 base pairs preceding the second c-myc exon. The provirus has a deletion of 80% of the viral genes but retains two intact long terminal repeats (LTRs). A segment of the viral env sequence is present in an inverted orientation. Elevated expression of c-myc, apparently directed by the 3' LTR, was detected. However, despite the presence of an intact 5' LTR, no viral transcripts were detected. Thus, the internal proviral rearrangement can affect 5' LTR transcription or stability of the message or both. This finding is in consonance with the view that proviral deletion plays an important role in the induction of bursal lymphomas by nonacute retroviruses.

Changes in minor transcripts from the alpha 1 and beta maj globin and glutathione peroxidase genes during erythropoiesis

We have analysed the transcriptional regulation of the murine alpha 1 and beta maj globin genes and the glutathione peroxidase (GSHPx) gene, which are all highly expressed during erythropoiesis. The levels of minor RNAs compared to the major message were monitored throughout differentiation within the erythroid lineage. For each gene, upstream transcripts arise from distinct clusters of sites which are regulated differently during differentiation: some occur only during early erythropoiesis, some occur early and persist to the terminal stages, while others accumulate later and roughly in parallel with the main RNA transcript. In addition, opposite strand transcripts from the GSHPx gene were found in increasing amounts during later stages of erythropoiesis. The initiation sites for specific subsets of these minor transcripts lie close to sequences known to be involved in globin gene regulation (i.e. the TATA, CAAT and the CACCCT boxes) or other conserved sequences; others lie close to developmentally regulated DNase I hypersensitive sites around the globin and GSHPx genes.

Dual tissue-specific expression of apo-AII is directed by an upstream enhancer

Apolipoprotein-AII (apo-AII) is one of a family of evolutionarily related proteins which play a crucial role in lipid transport and metabolism. The serum levels of human apo-AII have been shown to be inversely correlated to the incidence of coronary heart disease and its expression to be limited to the liver and intestine. Here we demonstrate that this dual tissue-specificity involves DNA sequences located in a 259 bp region centred 782 bp upstream from the transcription initiation site. These sequences function in an orientation-independent manner and are absolutely required for transcription from the apo-AII promoter. The regulatory region contains sequences which are homologous to the apo-AI, beta-globin and immunoglobulin gene promoters and to the immunoglobulin heavy-chain enhancer.

Human globin gene promoter sequences are sufficient for specific expression of a hybrid gene transfected into tissue culture cells

The contribution of the human globin gene promoters to tissue-specific transcription was studied by using globin promoters to transcribe the neo (G418 resistance) gene. After transfection into different cell types, neo gene expression was assayed by scoring colony formation in the presence of G418. In K562 human erythroleukemia cells, which express fetal and embryonic globin genes but not the adult beta-globin gene, the neo gene was expressed strongly from a fetal gamma- or embryonic zeta-globin gene promoter but only weakly from the beta promoter. In murine erythroleukemia cells which express the endogenous mouse beta genes, the neo gene was strongly expressed from both beta and gamma promoters. In two nonerythroid cell lines, human HeLa cells and mouse 3T3 fibroblasts, the globin gene promoters did not allow neo gene expression. Globin-neo genes were integrated in the erythroleukemia cell genomes mostly as a single copy per cell and were transcribed from the appropriate globin gene cap site. We conclude that globin gene promoter sequences extending from -373 to +48 base pairs (bp) (relative to the cap site) for the beta gene, -385 to +34 bp for the gamma gene, and -555 to +38 bp for the zeta gene are sufficient for tissue-specific and perhaps developmentally specific transcription.

Regulated expression of a complete human beta-globin gene encoded by a transmissible retrovirus vector

We introduced a human beta-globin gene into murine erythroleukemia (MEL) cells by infection with recombinant retroviruses containing the complete genomic globin sequence. The beta-globin gene was correctly regulated during differentiation, steady-state mRNA levels being induced 5- to 30-fold after treatment of the cells with the chemical inducer dimethyl sulfoxide. Studies using vectors which yield integrated proviruses lacking transcriptional enhancer sequences indicated that neither retroviral transcription nor the retroviral enhancer sequences themselves had any obvious effect on expression of the globin gene. Viral RNA expression also appeared inducible, being considerably depressed in uninduced MEL cells but approaching normal wild-type levels after dimethyl sulfoxide treatment. We provide data which suggest that the control point for both repression and subsequent activation of virus expression in MEL cells lies in the viral enhancer element.

Retroviral-mediated transfer of genomic globin genes leads to regulated production of RNA and protein

A high-titer amphotropic retroviral vector containing the neomycin resistance gene and a hybrid gamma-beta genomic human globin gene has been constructed. Mouse erythroleukemia cells infected with this virus were found to contain the full transcriptional unit of the transferred human globin gene by Southern blot analysis. These cells contain normally initiated, spliced, and terminated human globin mRNA. The human globin mRNA level increased 5- to 10-fold upon induction of the mouse erythroleukemia cells. Human globin chains were produced but only in a fraction of the cells as detected by immunofluorescent staining. A similar retrovirus containing a human beta-globin gene was used to transduce mouse erythroleukemia cells resulting in much higher levels of human globin synthesis than detected in mouse erythroleukemia cells transduced with the gamma-beta globin virus.

Nucleotide sequence of the delta-beta-globin intergenic segment in the macaque: structure and evolutionary rates in higher primates

A 5600-base-pair (bp) fragment including the beta-globin gene and about 4000 bp of its 5' flanking sequence was cloned from the DNA of Macaca cynomolgus (an Old World monkey), and the 5' flanking region was sequenced. Comparison with human, chimpanzee, mouse, rabbit, and Xenopus orthologous sequences reveals a tandemly repeated sequence called RS4 at the same position (about 500 bp 5' from the transcription start of the adult beta-globin gene) in all six species. We suggest that a tandemly repeated sequence has been maintained by functional constraints since the divergence between amphibians and reptiles. Excluding tandemly repeated sequences as well as about 400 nucleotides upstream from the cap site, the average base substitution frequencies among human, chimpanzee, and macaque intergenic sequences were calculated. They appear to be strongly correlated with the delta T50 values measured between the corresponding nuclear DNAs. They are also similar to base substitution frequencies calculated by Chang and Slightom (1984) at the pseudo-eta-globin locus. Thus, exclusion of sequences involved in specific modes of variation might allow the use of intergenic sequences for the accurate calculation of genetic distances. Using a time scale based on the dating of the Atlantic split, we estimate the base substitution rate of primate noncoding DNA to be 1.0 X 10(-9) substitution/site/year.

Delimiting regulatory sequences of the Drosophila melanogaster Ddc gene

We delimited sequences necessary for in vivo expression of the Drosophila melanogaster dopa decarboxylase gene Ddc. The expression of in vitro-altered genes was assayed following germ line integration via P-element vectors. Sequences between -209 and -24 were necessary for normally regulated expression, although genes lacking these sequences could be expressed at 10 to 50% of wild-type levels at specific developmental times. These genes showed components of normal developmental expression, which suggests that they retain some regulatory elements. All Ddc genes lacking the normal immediate 5'-flanking sequences were grossly deficient in larval central nervous system expression. Thus, this upstream region must contain at least one element necessary for this expression. A mutated Ddc gene without a normal TATA boxlike sequence used the normal RNA start points, indicating that this sequences is not required for start point specificity.

Regulated expression of a complete human beta-globin gene encoded by a transmissible retrovirus vector

We introduced a human beta-globin gene into murine erythroleukemia (MEL) cells by infection with recombinant retroviruses containing the complete genomic globin sequence. The beta-globin gene was correctly regulated during differentiation, steady-state mRNA levels being induced 5- to 30-fold after treatment of the cells with the chemical inducer dimethyl sulfoxide. Studies using vectors which yield integrated proviruses lacking transcriptional enhancer sequences indicated that neither retroviral transcription nor the retroviral enhancer sequences themselves had any obvious effect on expression of the globin gene. Viral RNA expression also appeared inducible, being considerably depressed in uninduced MEL cells but approaching normal wild-type levels after dimethyl sulfoxide treatment. We provide data which suggest that the control point for both repression and subsequent activation of virus expression in MEL cells lies in the viral enhancer element.

Cell-type-specific synthesis of murine immunoglobulin mu RNA from an adenovirus vector

The mouse immunoglobulin heavy-chain mu constant region gene was cloned into the early region 1B of an adenovirus type 5 vector to allow reproducible kinetics of expression of the mu gene in the presence of continuous host protein synthesis after infection by the recombinant. The immunoglobulin-adenovirus recombinant is helper independent in infecting human fibroblastic and B- and T-cell lines and expresses mu in a cell-type-specific manner. By Northern blot analysis, correctly polyadenylated and spliced E1B-mu S and E1B-mu m mRNAs are found to be equally abundant at steady state in fibroblasts. In contrast, and appropriately, only E1B-mu S mRNAs accumulate in a lambda light-chain-secreting myeloma cell line. Analysis of nascent transcripts pulse labeled in isolated nuclei demonstrates equimolar polymerase loading throughout the mu region in all cell types infected by mu-Ad. Thus, correct polyadenylation and splicing of E1B-mu S and E1B-mu m in fibroblasts does not require transcription termination in the region separating the mu S and mu m polyadenylation sites. Furthermore, differential expression of mu transcripts in the background of myeloma cells is regulated at the level of RNA processing and does not require the presence of the immunoglobulin heavy-chain enhancer or promoter element.

Androgen regulation by the long terminal repeat of mouse mammary tumor virus

Mouse mammary tumor virus (MMTV) has long been implicated in mouse mammary carcinogenesis, and it is now well established that the long terminal repeat (LTR) contains regulatory sequences responsible for glucocorticoid-mediated induction of viral RNA. However, we have demonstrated previously that androgens as well as glucocorticoids can regulate MMTV RNA in the S115 mouse mammary tumor cell line. To determine if androgens act directly on the LTR in these cells, plasmids were constructed with the MMTV LTR joined to the coding sequences of genes not normally expressed in the cells. Following transfection of these chimeric genes into S115 cells, we show that the expression of the genes is regulated by both androgens and glucocorticoids. Furthermore, hormonal regulation is also conferred by the LTR on the neighboring guanine phosphoribosyltransferase (gpt) gene. Thus, androgens can act on the LTR of MMTV when the appropriate receptors are present in the cells, and this interaction can influence the expression of additional adjacent genes.

A transcriptional enhancer located between adult beta-globin and embryonic epsilon-globin genes in chicken and duck

We have detected a transcriptional enhancer sequence downstream from the adult beta-globin (beta A-globin) genes of chicken and duck. DNA segments from the beta-globin coding and flanking sequences were cloned into expression vectors containing the SV40 promoter linked to either the T antigen gene or the cat gene. The expression of these genes was measured in a chicken erythroid cell line transfected with the recombinant plasmids. We found that segments located about 400 bp downstream from the poly(A) site of both the chicken and duck beta A-globin genes (and about 1.5 kb upstream from the embryonic epsilon-globin gene) stimulate transcription of the test genes about five-fold. In chicken essentially the same segment was also found by others to act as an erythroid cell-specific enhancer [Hesse et al., Proc. Natl. Acad. Sci. USA 83 (1986) 4312-4316; Choi and Engel, Nature 323 (1986) 731-734]. The sequence containing this enhancer is conserved in evolution. A high degree of homology, reaching 84% in a segment 180 bp in length, was found between chicken and duck despite an evolutionary divergence of 70 myr.

Comparison of the cis-acting control regions of two coordinately controlled genes involved in ethanol utilization in Aspergillus nidulans

The alcA and aldA genes of Aspergillus nidulans are regulated in exactly the same manner, being subject to positive control by the product of the alcR gene. We report the complete nucleotide sequence of the alcA gene and its 5' non-coding region, preliminary localization of the region involved in the regulation of alcA expression, and a detailed comparison of this region to the 5' non-coding region of aldA (Pickett et al., 1987). The 5' flanking regions of the genes contain six similar sequence elements. Three of these elements are located upstream from the messenger RNA start points and one is related to a sequence element found in the region responsible for ethanol induction of the yeast ADH2 gene (Beier et al., 1985). The other homologous elements are located within the messenger RNA leader and may be associated with selection of messenger RNA start points. The amino acid sequence of alcohol dehydrogenase I (348 residues) shows a significant level of homology with analogous sequences in other organisms. Gene alcA contains introns which are similar in size and structure to other fungal introns. We discuss the positions of the introns in alcA of A. nidulans with particular reference to the conservation of intron position in and the evolutionary assembly of enzymes which possess NAD-binding domains.

Human globin gene promoter sequences are sufficient for specific expression of a hybrid gene transfected into tissue culture cells

The contribution of the human globin gene promoters to tissue-specific transcription was studied by using globin promoters to transcribe the neo (G418 resistance) gene. After transfection into different cell types, neo gene expression was assayed by scoring colony formation in the presence of G418. In K562 human erythroleukemia cells, which express fetal and embryonic globin genes but not the adult beta-globin gene, the neo gene was expressed strongly from a fetal gamma- or embryonic zeta-globin gene promoter but only weakly from the beta promoter. In murine erythroleukemia cells which express the endogenous mouse beta genes, the neo gene was strongly expressed from both beta and gamma promoters. In two nonerythroid cell lines, human HeLa cells and mouse 3T3 fibroblasts, the globin gene promoters did not allow neo gene expression. Globin-neo genes were integrated in the erythroleukemia cell genomes mostly as a single copy per cell and were transcribed from the appropriate globin gene cap site. We conclude that globin gene promoter sequences extending from -373 to +48 base pairs (bp) (relative to the cap site) for the beta gene, -385 to +34 bp for the gamma gene, and -555 to +38 bp for the zeta gene are sufficient for tissue-specific and perhaps developmentally specific transcription.

Expression of Agrobacterium tumefaciens T-DNA gene 7 in Xenopus laevis oocytes

The expression of Agrobacterium tumefaciens T-DNA gene 7 was investigated in Xenopus laevis oocytes. Cloned DNA injected into oocytes consisted of T-DNA sequences derived from octopine type Ti plasmid B6-806 and T-DNA attached to plant DNA sequences at the left junction in crown gall tumors. Transcription initiation sites observed in oocytes were similar to those for transcript 7 in crown gall tumors. Quantitative differences in transcription occurred depending on the flanking sequences of the injected clones indicating that sequences upstream of the TATA box of T-DNA gene 7 affect the quantitative expression of this gene in Xenopus oocytes.

Upstream regions of the human cardiac actin gene that modulate its transcription in muscle cells: presence of an evolutionarily conserved repeated motif

Transfection into cultured cell lines was used to investigate the transcriptional regulation of the human cardiac actin gene. We first demonstrated that in both human heart and human skeletal muscle, cardiac actin mRNAs initiate at the identical site and contain the same first exon, which is separated from the first coding exon by an intron of 700 base pairs. A region of 485 base pairs upstream from the transcription initiation site of the human cardiac actin gene directs high-level transient expression of the bacterial chloramphenicol acetyltransferase gene in differentiated myotubes of the mouse C2C12 muscle cell line, but not in mouse L fibroblast or rat PC-G2 pheochromocytoma cells. Deletion analysis of this region showed that at least two physically separated sequence elements are involved, a distal one starting between -443 and -395 and a proximal one starting between -177 and -118, and suggested that these sequences interact with positively acting transcriptional factors in muscle cells. When these two sequence elements are inserted separately upstream of a heterologous (simian virus 40) promoter, they do not affect transcription but do give a small (four- to fivefold) stimulation when tested together. Overall, these regulatory regions upstream of the cap site of the human cardiac actin gene show remarkably high sequence conservation with the equivalent regions of the mouse and chick genes. Furthermore, there is an evolutionarily conserved repeated motif that may be important in the transcriptional regulation of actin and other contractile protein genes.

Partial purification of a nuclear protein that binds to the CCAAT box of the mouse alpha 1-globin gene

We enriched a fraction from nuclear extracts of murine erythroleukemia cells which contains a protein able to form stable complexes with the promoter region of the alpha 1-globin gene. Binding activity, which is present in mouse brain and a variety of cultured mouse and human cell lines, is not erythroid cell specific. Binding studies with alpha-globin gene promoter deletion mutants as well as DNase I footprinting and dimethyl sulfate protection studies showed that the factor bound specifically to the CCAAT box of the alpha 1 promoter. Enriched factor preparations exhibited weak binding to the promoter region of the beta maj-globin gene. This suggests that this protein could bind differentially to these two promoters in vivo. The enriched factor may be a ubiquitous nuclear protein involved in the differential regulation of the alpha 1- and beta maj-globin genes.

Differential transient and long-term expression of DNA sequences introduced into T-lymphocyte lines

We have used a protoplast fusion protocol to introduce the genes encoding neomycin phosphotransferase (neo) and chloramphenicol acetyltransferase (CAT) into murine and human T-lymphocyte lines. Plasmid constructs containing the neo gene under the control of the promoters from the Rous sarcoma virus long terminal repeat (RSV LTR), the SV40 early region, or the herpes simplex virus thymidine kinase gene (HSV TK) can stably transform each of three T-cell lines to G-418 resistance. The characteristic frequencies for different cell lines can differ by at least two orders of magnitude, although initial DNA uptake and transient expression are similar. In the two murine cell lines, low numbers of gene copies are retained in long-term transformants. Prior to integration, transient expression assays for cat or neo gene products reveal that the differences in intrinsic promoter strength of different constructs are further influenced by the coding sequences being transcribed. Thus, while transient expression of the neo protein is similar from both the Rous LTR and the SV40 early promoter, the Rous LTR directs synthesis of CAT protein at levels two orders of magnitude higher than those from the SV40 early promoter.

Delimiting regulatory sequences of the Drosophila melanogaster Ddc gene

We delimited sequences necessary for in vivo expression of the Drosophila melanogaster dopa decarboxylase gene Ddc. The expression of in vitro-altered genes was assayed following germ line integration via P-element vectors. Sequences between -209 and -24 were necessary for normally regulated expression, although genes lacking these sequences could be expressed at 10 to 50% of wild-type levels at specific developmental times. These genes showed components of normal developmental expression, which suggests that they retain some regulatory elements. All Ddc genes lacking the normal immediate 5'-flanking sequences were grossly deficient in larval central nervous system expression. Thus, this upstream region must contain at least one element necessary for this expression. A mutated Ddc gene without a normal TATA boxlike sequence used the normal RNA start points, indicating that this sequences is not required for start point specificity.

Differential expression of mouse beta/goat beta c, mouse beta/goat beta F, and mouse beta/goat epsilon II hybrid globin genes in murine erythroleukemia cells

We assembled three hybrid beta-globin genes by fusing the mouse beta-major promoter and initial transcribed region to one of three goat beta-like globin gene bodies: beta c (preadult), beta F (fetal), or epsilon II (embryonic). Thymidine kinase (tk)-deficient murine erythroleukemia (MEL) cells were cotransformed with one of these constructs and a separate plasmid bearing the tk gene. Half of the 24 cell lines containing either the mouse beta/goat beta c or mouse beta/goat beta F genes expressed the transferred genes at significant levels; in many cases the hybrid genes were, like the endogenous beta-globin genes, inducible with dimethyl sulfoxide. We obtained 13 cell lines containing the mouse beta/goat epsilon II hybrid gene, 6 of which were cotransfected with a mouse beta/human beta fusion gene known to function in MEL cells. In contrast to the results with the other fusion genes, the mouse beta/goat epsilon II hybrid was very poorly expressed: in two separate experiments, 0 of 13 and 2 of 13 lines showed significant mouse beta/goat epsilon II RNA levels after induction. In all these lines the endogenous mouse beta and cotransfected mouse beta/human beta genes were expressed. As an initial test of possible reasons for the inactivity of the mouse beta/goat epsilon II hybrid, we recloned this fusion gene into a tk-bearing plasmid, adjacent to the tk gene. Of 12 cell lines transformed with this plasmid, 11 produced mouse beta/goat epsilon II RNA; in 6 cases the expression was both strong and dimethyl sulfoxide inducible.

A 3' enhancer is required for temporal and tissue-specific transcriptional activation of the chicken adult beta-globin gene

The chicken adult beta-globin gene is one of the more intensively investigated developmentally regulated loci in higher eukaryotes. Detailed molecular analysis of the locus allows precise examination of the chromosomal changes that occur on activation of the gene during erythroid maturation. The best studied of these changes are the acquisition of DNase I hypersensitivity, developmentally correlated alteration of CpG-specific cytosine methylation patterns and in vitro assembly of erythroid-specific protein complexes 5' to the gene that mimics in vivo creation of the 5' DNase I hypersensitive 'region' lying 60 to 260 nucleotides 5' to the beta-globin cap site in red blood cell chromatin. Here we demonstrate that proximal beta-globin DNA sequences lying greater than 112 base pairs (bp) 5' to the cap site are not involved in determining the erythroid-specific induction characteristics of this gene in transient expression assays, whereas an enhancer sequence within a 300-bp PvuII fragment lying approximately 400 nucleotides 3' to the polyadenylation signal is intimately involved in determining the erythroid cell specificity and correct time of induction of beta-globin transcription during red cell maturation.

Alternate utilization of two regulatory domains within the Moloney murine sarcoma virus long terminal repeat

The Moloney murine sarcoma virus long terminal repeat (LTR) harbors two distinct positive activators of transcription, namely, a distal signal and an enhancer. In this report we demonstrate that infection by herpes simplex virus (HSV) can markedly affect the utilization of these two Moloney murine sarcoma virus transcription signals. We investigated the HSV-mediated trans-acting effects with two goals in mind: first, to gain insight into LTR function, and second, to probe the mechanisms used by HSV to establish its own transcription cascade. In mock-infected cells, LTR-mediated expression was heavily dependent on the Moloney murine sarcoma virus enhancer but was effectively distal signal independent. HSV infection mobilized the use of the LTR distal signal and concomitantly alleviated enhancer dependence. Indeed, enhancer function may actually be inhibited by HSV trans-acting factors. These results suggest that the two positive control signals of the Moloney murine sarcoma virus LTR facilitate transcriptional activation by two different pathways. We further observed that the identity of the structural gene driven by the LRT, as well as the state of integration of a transfected template, can exert a substantial effect on the response of a template to HSV infection. According to these findings, we propose a tentative model to account for the initial temporal shift of the HSV transcriptional cascade.

Expression of human beta-globin genes in transgenic mice: effects of a flanking metallothionein-human growth hormone fusion gene

In an attempt to place a human beta-globin gene in an open chromatin domain regardless of its site of integration in the mouse genome, we microinjected into fertilized mouse eggs a construct in which the human beta-globin gene and a mouse metallothionein-human growth hormone fusion gene were juxtaposed and oriented in opposite directions. Mice that developed from injected eggs and that grew larger than normal were analyzed for human beta-globin mRNA. The globin genes were not expressed in erythroid tissue but were expressed with the same tissue specificity as metallothionein-human growth hormone. These results suggest that sequences which control metallothionein-human growth hormone gene expression are capable of stimulating the expression of a flanking gene in an orientation-independent and tissue-specific manner. As a control for this experiment, we deleted the metallothionein-human growth hormone transcription unit and noted that the human beta-globin gene then was expressed at high levels with erythroid tissue specificity.