Three regions upstream from the cap site are required for efficient and accurate transcription of the rabbit beta-globin gene in mouse 3T6 cells

Identification of a duplication of the mouse Lyn gene

The Lyn gene encodes a PTK that is believed to participate in the transduction of signals from a variety of cell membrane receptors. Here we report the genomic organisation of the mouse Lyn gene and show that, while the promoter and exons 11-13 are present in single copy, sequences corresponding to the first coding exon are duplicated and this duplication extends into intron 10. Two sets of genomic clones representing the duplicated regions have been isolated and characterised. Nucleotide sequence analysis of these clones has revealed minimal sequence divergence between the two, suggesting that the duplication is a recent event. This is supported by Southern blot analysis of DNA from other mammalian species showing that the duplication is confined to the mouse. Aside from the duplicated sequences, the overall structure of the mouse Lyn gene is similar to that of other Src family members. These data suggest that the process of duplication which generated the Src family of PTK is an ongoing process and provide an insight into the molecular evolution of this group of genes.

Conservation of an AE3 Cl-/HCO3- exchanger cardiac-specific exon and promoter region and AE3 mRNA expression patterns in murine and human hearts

A cardiac-specific variant of the rat AE3 Cl-/HCO3- exchanger mRNA is transcribed from a promoter located in the sixth intron of a larger transcription unit expressed in brain and other tissues. The cardiac mRNA contains an alternative first exon encoding a 73-amino acid NH2-terminal sequence that replaces the first 270 amino acids of the brain AE3 variant. The present study was conducted to determine whether the cardiac-specific promoter region and exon are conserved in other species and to examine the expression patterns of AE3 mRNAs in adult tissues and during development. Analysis of murine and human genomic clones showed that both contain counterparts of the rat alternative exon. The cardiac promoter region is highly conserved in all three species and contains several potential transcription factor binding sites, including consensus MCAT and E-box sequences. Tissue-specific and developmental patterns of AE3 gene expression were examined by Northern blot hybridization. Mouse and human, like the rat, express both the 3.6-kb cardiac-specific AE3 mRNA and a 4.4-kb AE3 transcript found in brain, heart, and other tissues. Levels of the cardiac-specific transcript in mouse heart increase 17-fold between the fetal and adult stages, while the amount of the longer AE3 mRNA in heart decreases substantially. Furthermore, although the cardiac-specific mRNA is expressed in both atria and ventricles of mouse heart, the longer transcript is confined to the atria. These results suggest that the two AE3 variants have distinct roles in cardiac function and that the mechanisms regulating their expression are different.

TFIIIC determines RNA polymerase III specificity at the TATA-containing yeast U6 promoter

The gene encoding yeast U6 snRNA that is transcribed by RNA polymerase III (Pol III) contains both a TATA box upstream of the transcription start site and a downstream binding site for the factor TFIIIC. This juxtaposition of elements typical of both Pol II- and Pol III-transcribed genes raises the question of how polymerase specificity is determined. The upstream U6 promoter containing the TATA box and transcription start site was shown previously to be transcribed by Pol III in vitro. We therefore tested whether the upstream promoter of yeast U6 encodes Pol III specificity. One model is that polymerase specificity is conferred by the homologous Pol II and Pol III transcription factors TFIIB and BRF1. However, we found no specificity in the binding of BRF1 or TFIIB to TATA-containing promoters of genes specifically transcribed by Pol III or Pol II. Yeast strains deficient for Pol II or Pol III transcription were employed to examine U6 polymerase specificity in vivo. We find that the U6 upstream promoter is Pol II-specific in vivo and is converted to Pol III specificity by TFIIIC. Thus, preferential recruitment of TFIIIB by TFIIIC probably excludes the Pol II general factors and promotes Pol III transcription, thereby determining polymerase specificity.

Sequence polymorphism in the HLA-B promoter region

Transcription of major histocompatibility complex class I genes is controlled by the class I regulatory complex in the 5' flanking region. To investigate the molecular basis of this region, we studied the polymorphism of the promoter of the HLA-B locus extending from the ATG transcription initiation signal to -284 base pairs (bp) which includes a number of cis-acting elements: interferon response sequence (IRS), enhancer A and enhancer B. Genomic DNA from 35 homozygous cell lines from the 10th International Histocompatibility Workshop and from eight heterozygous panel members was amplified using two primers designed to specifically amplify the HLA-B locus. The double-stranded polymerase chain reaction products were sequenced using the cycle sequencing technique and an ABI 373A automatic sequencer. Promoter sequences of thirty-one different HLA-B alleles were determined in this study. Within the 284 bp upstream of the ATG signal, base substitutions were observed in 23 different nucleotide positions. Our study shows a high degree of polymorphism of the HLA-B promoter region, but conserved sequences of the known cis-acting elements with the exception of enhancer B in which there are two base substitutions for B7 and B42 (position -93 and position -95). The 23 polymorphic sites can be grouped into 12 different HLA-B promoter types (groups A to M) for 31 HLA-B locus alleles. Some of the groups of alleles sharing the same promoter sequence such as, for example, group A with B51, B52, B53, and B35, might have been predicted on the basis of serological similarity and/or exon 2, 3 sequence. In other groups, such as G (B18, B37, B27), it could not have been anticipated from serological experience that B18 and B27 carry the same promoter. Several sequencing errors were detected in the HLA-B promoter sequences published previously.

Characterization of the human tryptophan hydroxylase gene promoter. Transcriptional regulation by cAMP requires a new motif distinct from the cAMP-responsive element

We isolated and sequenced 2,117 nucleotides of the promoter region of the human tryptophan hydroxylase (TPH) gene. Transient transfection in pinealocyte cultures and PC12 cells was used to investigate the human TPH (hTPH) gene promoter activity and its regulation by the cAMP signaling pathway. A region of 2,117 base pairs upstream of the transcription initiation site of the hTPH gene efficiently directed the transcription of a luciferase reporter gene but not in a cell-specific manner. The hTPH promoter activity was significantly enhanced by a cyclic AMP analog in the two cell types. Deletion analysis showed that the promoter region from -73 to +2 is sufficient to direct cAMP-dependent transcription, although it does not contain a motif exhibiting a significant identity to the cAMP-responsive element (CRE) or AP-2 binding site. Following site-directed mutagenesis of the region between -73 and -51, an inverted CCAAT box motif was identified as essential for cAMP inducibility of the hTPH promoter. This sequence between -73 and -51 alone allowed cAMP enhancement of transcription when fused to a heterologous promoter. Additionally, electrophoretic mobility shift assays showed that a specific protein-DNA complex is formed between an oligonucleotide corresponding to the inverted CCAAT box motif and nuclear proteins from pinealocytes treated or not treated with cAMP. Thus cAMP responsiveness of hTPH gene expression is mediated by a cis-acting element, which shares strong identity with an inverted CCAAT box and which binds to a constitutively produced nuclear factor.

The erythroid Krüppel-like factor transactivation domain is a critical component for cell-specific inducibility of a beta-globin promoter

Erythroid Krüppel-like factor (EKLF) is an erythroid cell-specific DNA-binding protein that activates transcription from the beta-globin CACCC element, a functionally important and evolutionarily conserved component of globin as well as other erythroid cell-specific promoters and enhancers. We have attempted to elucidate the molecular role of EKLF in erythrocyte-specific transcriptional activation. First, in vivo and in vitro analyses have been used to demonstrate that the level of activation by EKLF is dependent on the orientation and number of CACCC elements, that EKLF contains separable activation and DNA-binding domains, and that the EKLF proline-rich region is a potent activator in CV-1 cells when fused to a nonrelated DNA-binding module. Second, we have established a transient assay in murine erythroleukemia cells in which reproducible levels of a reporter can be induced when linked to a locus control region enhancer-beta-globin promoter and in which induction is abolished when the promoter CAC site is mutated to a GAL site. Third, we demonstrate that the EKLF transactivation region, when fused to the GAL DNA-binding domain, can restore inducibility to this mutated construct and that this inducibility exhibits activator-, promoter-, and cell-type specificity. These results demonstrate that EKLF provides a crucial transactivation function for globin expression and further reinforce the idea that EKLF is an important regulator of CACCC element-directed transcription in erythroid cells.

Role of erythroid Kruppel-like factor in human gamma- to beta-globin gene switching

Erythroid Kruppel-like factor (EKLF) is an erythroid-specific transcription factor that contains zinc finger domains similar to the Kruppel protein of Drosophila melanogaster. Previous studies demonstrated that EKLF binds to the CACCC box in the human beta-globin gene promoter and activates transcription. CACCC box mutations that cause severe beta-thalassemias in humans inhibit EKLF binding. Results described in this paper suggest that EKLF functions predominately in adult erythroid tissue. The EKLF gene is expressed at a 3-fold higher level in adult erythroid tissue than in fetal erythroid tissue, and the EKLF protein binds to the human beta-globin promoter 8-fold more efficiently than to the human gamma-globin promoter. Co-transfection experiments in the human fetal-like erythroleukemia cell line K562 demonstrate that over-expression of EKLF activates a beta-globin reporter construct 1000-fold; a linked gamma-globin reporter is activated only 3-fold. Mutation of the beta-globin CACCC box severely inhibits activation. These results demonstrate that EKLF is a developmental stage-enriched protein that preferentially activates human beta-globin gene expression. The data strongly suggest that EKLF is an important factor involved in human gamma- to beta-globin gene switching.

A novel myogenic regulatory circuit controls slow/cardiac troponin C gene transcription in skeletal muscle

The slow/cardiac troponin C (cTnC) gene is expressed in three distinct striated muscle lineages: cardiac myocytes, embryonic fast skeletal myotubes, and adult slow skeletal myocytes. We have reported previously that cTnC gene expression in cardiac muscle is regulated by a cardiac-specific promoter/enhancer located in the 5' flanking region of the gene (bp -124 to +1). In this report, we demonstrate that the cTnC gene contains a second distinct and independent transcriptional enhancer which is located in the first intron. This second enhancer is skeletal myotube specific and is developmentally up-regulated during the differentiation of myoblasts to myotubes. This enhancer contains three functionally important nuclear protein binding sites: a CACCC box, a MEF-2 binding site, and a previously undescribed nuclear protein binding site, designated MEF-3, which is also present in a large number of skeletal muscle-specific transcriptional enhancers. Unlike most skeletal muscle-specific transcriptional regulatory elements, the cTnC enhancer does not contain a consensus binding site (CANNTG) for the basic helix-loop-helix (bHLH) family of transcription factors and does not directly bind MyoD-E12 protein complexes. Despite these findings, the cTnC enhancer can be transactivated by overexpression of the myogenic bHLH proteins, MyoD and myogenin, in C3H10T1/2 (10T1/2) cells. Electrophoretic mobility shift assays demonstrated changes in the patterns of MEF-2, CACCC, and MEF-3 DNA binding activities following the conversion of 10T1/2 cells into myoblasts and myotubes by stable transfection with a MyoD expression vector. In particular, MEF-2 binding activity was up-regulated in 10T1/2 cells stably transfected with a MyoD expression vector only after these cells fused and differentiated into skeletal myotubes. Taken together, these results demonstrated that distinct lineage-specific transcriptional regulatory elements control the expression of a single myofibrillar protein gene in fast skeletal and cardiac muscle. In addition, they show that bHLH transcription factors can indirectly transactivate the expression of some muscle-specific genes.

A novel myogenic regulatory circuit controls slow/cardiac troponin C gene transcription in skeletal muscle

The slow/cardiac troponin C (cTnC) gene is expressed in three distinct striated muscle lineages: cardiac myocytes, embryonic fast skeletal myotubes, and adult slow skeletal myocytes. We have reported previously that cTnC gene expression in cardiac muscle is regulated by a cardiac-specific promoter/enhancer located in the 5' flanking region of the gene (bp -124 to +1). In this report, we demonstrate that the cTnC gene contains a second distinct and independent transcriptional enhancer which is located in the first intron. This second enhancer is skeletal myotube specific and is developmentally up-regulated during the differentiation of myoblasts to myotubes. This enhancer contains three functionally important nuclear protein binding sites: a CACCC box, a MEF-2 binding site, and a previously undescribed nuclear protein binding site, designated MEF-3, which is also present in a large number of skeletal muscle-specific transcriptional enhancers. Unlike most skeletal muscle-specific transcriptional regulatory elements, the cTnC enhancer does not contain a consensus binding site (CANNTG) for the basic helix-loop-helix (bHLH) family of transcription factors and does not directly bind MyoD-E12 protein complexes. Despite these findings, the cTnC enhancer can be transactivated by overexpression of the myogenic bHLH proteins, MyoD and myogenin, in C3H10T1/2 (10T1/2) cells. Electrophoretic mobility shift assays demonstrated changes in the patterns of MEF-2, CACCC, and MEF-3 DNA binding activities following the conversion of 10T1/2 cells into myoblasts and myotubes by stable transfection with a MyoD expression vector. In particular, MEF-2 binding activity was up-regulated in 10T1/2 cells stably transfected with a MyoD expression vector only after these cells fused and differentiated into skeletal myotubes. Taken together, these results demonstrated that distinct lineage-specific transcriptional regulatory elements control the expression of a single myofibrillar protein gene in fast skeletal and cardiac muscle. In addition, they show that bHLH transcription factors can indirectly transactivate the expression of some muscle-specific genes.

The ht beta gene encodes a novel CACCC box-binding protein that regulates T-cell receptor gene expression

A gene encoding a novel CACCC box-binding protein that binds to the promoter region of the human T-cell receptor (TCR) V beta 8.1 gene and the mouse TCR alpha gene silencer has been cloned. This gene, termed ht beta, contains four zinc fingers of the class Cys2-X12-His2 that may be responsible for DNA binding and a highly negatively charged region that defines a putative transcriptional activation domain. Analysis of the expression of ht beta mRNA revealed similar expression levels and patterns in various cell lines. The bacterially expressed ht beta protein can bind to the CACCC box in both the human TCR V beta 8.1 gene promoter and the mouse TCR alpha gene silencer. The CACCC box is essential for efficient transcription of the V beta 8.1 promoter. Cotransfection with an ht beta expression plasmid and a reporter vector indicated that ht beta can activate human TCR V beta 8.1 gene transcription. ht beta also is able to counteract the silencing effect of the mouse TCR alpha gene silencer. The CACCC box has been found in almost all V beta 8.1 gene subfamily members and in both TCR alpha and beta gene enhancers in humans and mice. These results suggest that the CACCC box-binding protein may have an important regulatory function for TCR gene expression in alpha beta T cells versus gamma delta T cells.

The ht beta gene encodes a novel CACCC box-binding protein that regulates T-cell receptor gene expression

A gene encoding a novel CACCC box-binding protein that binds to the promoter region of the human T-cell receptor (TCR) V beta 8.1 gene and the mouse TCR alpha gene silencer has been cloned. This gene, termed ht beta, contains four zinc fingers of the class Cys2-X12-His2 that may be responsible for DNA binding and a highly negatively charged region that defines a putative transcriptional activation domain. Analysis of the expression of ht beta mRNA revealed similar expression levels and patterns in various cell lines. The bacterially expressed ht beta protein can bind to the CACCC box in both the human TCR V beta 8.1 gene promoter and the mouse TCR alpha gene silencer. The CACCC box is essential for efficient transcription of the V beta 8.1 promoter. Cotransfection with an ht beta expression plasmid and a reporter vector indicated that ht beta can activate human TCR V beta 8.1 gene transcription. ht beta also is able to counteract the silencing effect of the mouse TCR alpha gene silencer. The CACCC box has been found in almost all V beta 8.1 gene subfamily members and in both TCR alpha and beta gene enhancers in humans and mice. These results suggest that the CACCC box-binding protein may have an important regulatory function for TCR gene expression in alpha beta T cells versus gamma delta T cells.

CCACC-binding or simian-virus-40-protein-1-binding proteins cooperate with human GATA-1 to direct erythroid-specific transcription and to mediate 5' hypersensitive site 2 sensitivity of a TATA-less promoter

Previous studies have shown that a -112 to +78 DNA fragment from the erythroid promoter of the human porphobilinogen deaminase (PBGD) gene has erythroid-specific activity. This PBGD-(-112 to +78) promoter contains a CCACC binding site (position -100), a GATA binding site (position -70) and an initiator element around the cap site. Using a cotransfection assay, we find that the human factor GATA-1 trans-activates the PBGD-(-112 to +78) promoter in non-erythroid cells. We show that, if trans-activation is abolished by mutations that destroy either the -100 CCACC binding or the -70 GATA binding sites, replacement of the -100 CCACC binding site by a simian-virus-40-protein-1 (Sp1) binding site maintains both the erythroid-specific activity of this promoter and the human GATA-1 trans-activation. Thus, human GATA-1 acts on the PBGD promoter in association with Sp1 or CCACC binding proteins. This PBGD-(-112 to +78) promoter is activated 20-fold by a cis-linked 5' hypersensitive site 2 (5'HS-2) of the human beta-globin locus control region. This activation depends on the -70 GATA and -100 CCACC or Sp1 binding sites. When a longer -714 to +78 fragment of the PBGD promoter is used, the -70 GATA mutant still displays erythroid-specific activity and is cis-activated by the 5'HS-2 enhancer, while the -100 CCACC mutant is completely inactive in the absence or in the presence of the 5'HS-2 enhancer. Thus, the -100 CCACC binding site is indispensable for the correct activity and sensitivity of the human PBGD promoter to the 5'HS-2 enhancer, whereas the -70 GATA binding site can functionally be replaced by upstream cis-acting elements.

Analysis of the promoter sequence and the transcription initiation site of the mouse 5-HT1C serotonin receptor gene

The serotonin 1c (5-HT1C) receptor is found in many brain regions, but is particularly enriched on the epithelial cells of the choroid plexus. A major challenge in neurobiology is to delineate the molecular processes that regulate the specific pattern of neuronal gene expression in the brain. As an initial step towards identifying cis-acting DNA sequences that control the expression of the 5-HT1C receptor, we have isolated the promoter sequence of its gene. Sequence analysis of a 1.8 kb fragment indicated that the 3' end of this fragment overlaps with the 5' untranslated region of the 5-HT1C receptor mRNA, and primer extension using mouse brain poly(A)+ RNA mapped the transcription initiation site within this fragment. There are a number of sequence elements upstream from the transcription initiation site that are homologous to regulatory elements found in other eucaryotic genes. To determine the promoter activity, a plasmid was constructed that contains this fragment as promoter region and the cDNA for the 5-HT1C receptor as the reporter. When injected into the nucleus of Xenopus oocytes, this construct resulted in functional expression of the reporter gene. Primer extension using the RNA extracted from the injected oocytes indicated a single transcription initiation site of the reporter mRNA. These results suggest that the 5-HT1C receptor was functionally expressed under the promoter activity of the 1.8 kb 5' sequence of its gene. This system will be useful for further analysis of the cis-acting elements in the promoter region of the 5-HT1C receptor gene and the trans-acting factors that regulate tissue-specific expression of the receptor.

Discrimination among potential activators of the beta-globin CACCC element by correlation of binding and transcriptional properties

Adult beta-globin-like promoters contain a cis-acting element, CCACACCC, that is conserved across species and is required for wild-type levels of transcription. We have studied the contribution of this element and proteins that interact with it to activate beta-globin transcription. We found that an erythroid-like cell line, MEL, contains several proteins that specifically bind the CACCC element. By comparing the DNA-binding properties of promoters with mutations in the CACCC element with the transcriptional activities of these mutant promoters, we found that two CACCC-binding proteins did not bind to mutant promoters that direct decreased levels of transcription. One of these proteins is the transcriptional activator Sp1, and the other we have designated CACD (CACCC-binding species D). We subjected CACD to a binding site selection procedure and obtained high-affinity CACD binding sites that are identical to that of the beta-globin CACCC element. This result, combined with our finding that CACD binds the CACCC element with a higher affinity than does Sp1, argues that the CACCC element is a target of CACD rather than Sp1. The strategy of correlating the results of a binding site selection experiment with those of in vivo expression and in vitro binding studies may allow evaluation of the relative potential of different proteins to activate transcription through a single cis-acting site.

TATA box mutations in the Schizosaccharomyces pombe nmt1 promoter affect transcription efficiency but not the transcription start point or thiamine repressibility

The nmt1 gene of Schizosaccharomyces pombe is highly expressed and subject to transcriptional repression by thiamine. The nmt1 promoter, in common with other strong promoters in this organism, contains a canonical sequence element, 5'-ATATATAAA, located 25 bp upstream from the transcription start point (tsp). We have made stepwise deletions of the TATA box and quantitated the effects of the mutations by assaying the expression of the chloramphenicol acetyltransferase (CAT)-encoding gene (cat) cloned downstream. Our results demonstrate that progressive truncation of the TATA box results in a concomitant decrease in promoter strength as judged both by the loss of CAT activity in cell extracts and by a reduction in the steady-state level of cat mRNA. Both the induced level and the residual, repressed level of expression observed in the presence of thiamine are similarly down-regulated. On the other hand, even in the most extreme mutant, the tsp is unaffected, suggesting that other elements in the nmt1 promoter are important in determination of the tsp. The properties of the modified promoters have made them useful for extending the range of the pREP inducible expression vectors.

The arthropod initiator: the capsite consensus plays an important role in transcription

Approximately 25% of arthropod RNA polymerase II-transcribed promoters contain one or more copies of the sequence TCAGT beginning within the interval (-10, +10). The clear statistical overrepresentation of this sequence and, to a lesser extent, of its cognates ACAGT, GCAGT, and TCATT, implies that they may be significant promoter elements. Their collective sequence similarity to vertebrate initiators (Inrs) of the TdT class suggests that the vertebrate and arthropod elements are homologous. Prior work in vertebrate systems has emphasized the role of the Inr in promoters lacking TATA boxes, where it can serve as an alternate staging site for polymerase II initiation. However, it is clear that the Inr sequence is by no means restricted to TATA-deficient promoters. Functional tests using the TATA-containing Drosophila gene Eip28/29 support the idea that the Inr is a facultative promoter element, required for efficient transcription under some conditions. For example, the Inr protects basal expression of Eip28/29 from the silencing effect of ecdysone response elements. In addition, the Inr is required for the function of an enhancer of basal activity in Eip28/29. We conclude that Inrs are promoter elements found sporadically throughout the higher eukaryotes, that the requirement for an Inr depends upon the array of other promoter elements which may be present in a given gene, and that Inrs may permit enhancers to discriminate among promoters.

Discrimination among potential activators of the beta-globin CACCC element by correlation of binding and transcriptional properties

Adult beta-globin-like promoters contain a cis-acting element, CCACACCC, that is conserved across species and is required for wild-type levels of transcription. We have studied the contribution of this element and proteins that interact with it to activate beta-globin transcription. We found that an erythroid-like cell line, MEL, contains several proteins that specifically bind the CACCC element. By comparing the DNA-binding properties of promoters with mutations in the CACCC element with the transcriptional activities of these mutant promoters, we found that two CACCC-binding proteins did not bind to mutant promoters that direct decreased levels of transcription. One of these proteins is the transcriptional activator Sp1, and the other we have designated CACD (CACCC-binding species D). We subjected CACD to a binding site selection procedure and obtained high-affinity CACD binding sites that are identical to that of the beta-globin CACCC element. This result, combined with our finding that CACD binds the CACCC element with a higher affinity than does Sp1, argues that the CACCC element is a target of CACD rather than Sp1. The strategy of correlating the results of a binding site selection experiment with those of in vivo expression and in vitro binding studies may allow evaluation of the relative potential of different proteins to activate transcription through a single cis-acting site.

Long-term sensitization training in Aplysia leads to an increase in the expression of BiP, the major protein chaperon of the ER

Long-term memory for sensitization of the gill- and siphon-withdrawal reflexes in Aplysia californica requires RNA and protein synthesis. These long-term behavioral changes are accompanied by long-term facilitation of the synaptic connections between the gill and siphon sensory and motor neurons, which are similarly dependent on transcription and translation. In addition to showing an increase in over-all protein synthesis, long-term facilitation is associated with changes in the expression of specific early, intermediate, and late proteins, and with the growth of new synaptic connections between the sensory and motor neurons of the reflex. We previously focused on early proteins and have identified four proteins as members of the immunoglobulin family of cell adhesion molecules related to NCAM and fasciclin II. We have now cloned the cDNA corresponding to one of the late proteins, and identified it as the Aplysia homolog of BiP, an ER resident protein involved in the folding and assembly of secretory and membrane proteins. Behavioral training increases the steady-state level of BiP mRNA in the sensory neurons. The increase in the synthesis of BiP protein is first detected 3 h after the onset of facilitation, when the increase in overall protein synthesis reaches its peak and the formation of new synaptic terminals becomes apparent. These findings suggest that the chaperon function of BiP might serve to fold proteins and assemble protein complexes necessary for the structural changes characteristic of long-term memory.

Regulatory mutations and human genetic disease

Mutations in gene promoter/regulatory regions represent an important class of lesion causing human genetic disease. Such mutations are associated with either increases or decreases in transcriptional activity mediated by the altered binding behaviour of trans-acting protein factors to specific DNA sequences in the promoter region. Although most promoter mutations are individually very infrequent, some occur at polymorphic frequencies. Both categories of lesion are likely to be important in clinical medicine and their study has already led to new insights into the mechanisms underlying the regulation of human genes.

Long-term sensitization training in Aplysia leads to an increase in calreticulin, a major presynaptic calcium-binding protein

Long-term memory for sensitization in Aplysia requires new protein and RNA synthesis. Here, we identify a late protein as calreticulin, the major Ca(2+)-binding protein of the lumen of the endoplasmic reticulum. An antiserum against Aplysia calreticulin reveals an enrichment of calreticulin immunoreactivity in presynaptic varicosities. Quantitative S1 nuclease analysis indicates that the steady-state level of calreticulin mRNA in Aplysia sensory neurons increases during the maintenance phase of long-term sensitization. The finding that this mRNA increases in expression late, some time after training, is consistent with the idea that long-term neuromodulatory changes underlying sensitization may depend on a cascade of gene expression in which the induction of early regulatory genes leads to the expression of late effector genes.

Organization of non-vertebrate globin genes

The organization of non-vertebrate globin genes exhibits substantially more variability than the three-exon, two-intron structure of the vertebrate globin genes. (1) The structures of genes of the single-domain globin chains of the annelid Lumbricus and the mollusc Anadara, and the globin gene coding for the two-domain chains of the clam Barbatia, are similar to the vertebrate plan. (2) Genes for single-domain chains exist in bacteria and protozoa. Although the globin gene is highly expressed in the bacterium Vitreoscilla, the putative globin gene hmp in E. coli, which codes for a chimeric protein whose N-terminal moiety of 139 residues contains 67 residues identical to the Vitreoscilla globin, may be either unexpressed or expressed at very low levels, despite the presence of normal regulatory sequences. The DNA sequence of the globin gene of the protozoan Paramecium, determined recently by Yamauchi and collaborators, appears to consist of two exons separated by a short intron. (3) Among the lower eukaryotes, the yeasts Saccharomyces and Candida have chimeric proteins consisting of N-terminal globin and C-terminal flavoprotein moieties of about the same size. The structure of the gene for the chimeric protein of Saccharomyces exhibits no introns. According to Riggs, the presence of chimeric proteins in E. coli and other prokaryotes, such as Alcaligenes and Rhizobium, as well as in yeasts, suggests a previously unrecognized evolutionary pathway for hemoglobin, namely that of a multipurpose heme-binding domain attached to a variety of unrelated proteins with diverse functions. (4) The published globin gene sequences of the insect larva Chironomus have an intron-less structure and are present as clusters of multiple copies; the expression of the globin genes is tissue and developmental stage-specific. Furthermore, the expression of many of these genes has not yet been demonstrated despite the presence of apparently normal regulatory sequences in the two flanking regions. Unexpectedly, Bergtrom and collaborators have recently shown that at least three Ctt globin II beta genes contain putative introns. (5) Pohajdak and collaborators have found a seven-exon and six-intron structure for the globin gene of the nematode Pseudoterranova which codes for a two-domain globin chain. Although the second and fourth introns of the N-terminal domain correspond to the two introns found in vertebrate globin genes, the position of the third intron is close to that of the central intron in plant hemoglobins.(ABSTRACT TRUNCATED AT 400 WORDS)

Mouse dopamine beta-hydroxylase: primary structure deduced from the cDNA sequence and exon/intron organization of the gene

Genomic clones for mouse dopamine beta-hydroxylase (DBH) were isolated from two genomic libraries derived from DBA/2J and 129/SV mouse strains, by plaque hybridization with the human DBH cDNA probe. Subsequently, cDNA encoding mouse DBH was amplified with reverse transcription-polymerase chain reaction (RT-PCR) method using primers corresponding to 5'- and 3'-portions of the mouse DBH mRNA, subcloned into a plasmid vector, and subjected to nucleotide sequence analysis. The clone encoded a protein of 621 amino acids with a calculated molecular mass of 70,186 daltons. The predicted amino acid sequence of mouse DBH showed 87%, 80% and 79% identities with the rat, bovine and human enzymes, respectively. Several potential amino acid sequences that are involved in the posttranslational modification and catalytic function of DBH were identified in mouse DBH protein. Nucleotide sequence analysis of the overlapping genomic clones showed that the mouse DBH gene was composed of 12 exons about 17 kb in length. Typical TATA and CCAAT boxes were observed in the 5'-upstream region of the gene. Northern blot analysis of adrenal gland RNA detected a single size species of the mouse DBH mRNA.

Mutational analysis of a plant heat shock element

A total of 32 mutations were generated within the TATA-proximal site 1 (-72 to -47) of soybean heat shock gene Gmhsp17.5E in order to functionally define the optimal configuration of sequences within the heat shock element (HSE). Mutants were tested in vivo utilizing sunflower tumors transformed by a T-DNA based vector. Promoter activity was determined by S1 nuclease hybrid protection analysis of tumor transcripts. A total of five repeats (5'-nGAAn-3' or 5'-nTTCn-3') which comprise the HSE at site 1 were required for full transcription induction by heat stress. Analysis of non-conserved bases flanking the central trinucleotide block indicated that 5'-aGAAg'-3' is the optimum sequence for the 5 bp repeat.

Regulation of transcription of immunoglobulin germ-line gamma 1 RNA: analysis of the promoter/enhancer

Antibody class switching is achieved by recombinations between switch (S) regions which consist of tandemly repeated sequences located 5' to Ig heavy chain constant (CH) region genes. RNA transcripts from specific unrearranged or germ-line Ig CH genes are induced in IgM+ B cells prior to their undergoing class switch recombination to the same CH genes. Thus, the antibody class switch appears to be directed by induction of accessibility, as assayed by transcription of germ line CH genes. For example, IL-4 induces transcripts from the mouse germ-line C gamma 1 and C epsilon genes to which it also directs switch recombination. We report here that the 150 bp region upstream of the first initiation site of RNA transcribed from the murine germ-line C gamma 1 gene, contains promoter and enhancer elements responsible for basal level transcription and inducibility by anti-Ig phorbol myristate acetate (PMA) and for synergy of these inducers with IL-4 in a surface IgM+ B cell line, L10A6.2 and a surface IgG2a+ B cell line, A20.3. Linker-scanning mutations demonstrated that multiple interdependent elements are required for inducibility by PMA and also for synergy with IL-4. Within the 150 bp region are several consensus sequences that bind known or putative transcription factors, including a C/EBP binding site--IL-4 responsive element, four CACCC boxes, a PU box, a TGF beta inhibitory element (TIE), an alpha beta-interferon response element (alpha beta-IRE) and an AP-3 site. The relationship between transcription regulated by these elements and the regulation of endogenous germ-line gamma 1 transcripts and switching to IgG1 is discussed.

Upstream box/TATA box order is the major determinant of the direction of transcription

Mammalian gene promoters for transcription by RNA polymerase II are typically organized in the following order: upstream sequence motif(s)/TATA box/initiation site. Here we report studies in which the order, orientation and DNA sequences of these three elements are varied to determine how these affect polarity of transcription. We have constructed promoters with an 'octamer' upstream sequence ATTTGCAT (or its complement ATGCAAAT) in combination with several different TATA boxes and initiation (cap) sites, and tested these promoters in transfection experiments with cultured cells. TATA boxes derived from the adenovirus major late promoter (TATAAAA), immunoglobulin kappa light chain (TTATATA) and heavy chain (TAAATATA) promoter functioned equally well or even better when inverted. Only the beta-globin TATA box (CATAAAA) was poorly active when inverted. In addition, a symmetrical TATA box (TATATATA) derived from a casein gene was very active. Our results suggest that the asymmetry of most TATA boxes (consensus TATAAAA) is not a primary determinant of the polarity of transcription. We also found that the initiation (cap) site, which usually consists of an adenine embedded in a pyrimidine-rich region (PyPyCAPyPyPyPyPy), was permissive towards sequence alterations; even a randomly composed sequence worked well. However, an inverted, hence purine-rich, cap site reduced transcript levels to 1/7th, as did an oligo G sequence. Irrespective of the presence of a cap site, the configuration: 'TATA box/octamer' yielded a strong leftward, rather than rightward transcription. From this, we conclude that the polarity of transcription is primarily determined by the linear order of an upstream sequence relative to a TATA box, rather than by the individual orientations of either of these two elements.

Control regions of an archaeal gene. A TATA box and an initiator element promote cell-free transcription of the tRNA(Val) gene of Methanococcus vannielii

To identify the DNA sequences required for initiation of transcription in archaea, the 5'-flanking region of the tRNA(Val) gene of Methanococcus vannielii was modified by deletions, restructuring and site-directed mutagenesis, and the tRNA encoding sequence was replaced by a fortuitous Escherichia coli sequence. The effects of these mutations on promoter function were tested in an homologous cell-free transcription system. The DNA region from position -35 to +9 relative to the transcription start site was sufficient for maximal initiation of cell-free transcription. Removal of the DNA region between -35 and -30 reduced initiation by a factor of 2. Deletions extending to position -24 almost completely abolished specific transcription. Analysis of 16 site-specific mutations in the region from -33 to +2 provided evidence that a conserved A + T-rich sequence (TATA box), centered at -25, is essential for initiation of transcription. Single point mutations in six positions of the TATA box reduced initiation of transcription from 0.2 to 0.01 of wild-type levels. A second conserved motif at the transcription start site (consensus ATGC) could be replaced by some sequences containing a pyrimidine-purine dinucleotide but appeared necessary for a maximal rate of gene transcription. Mutations altering the spacing between the two conserved elements demonstrated that initiation occurs at a strictly defined distance of 22 to 27 base-pairs downstream from the TATA box. Our results support the conclusion that the TATA box is the major DNA region mediating promoter recognition, influencing the efficiency of transcription and specifying the site of transcription initiation. This Methanococcus promoter element closely resembles in structure and function the TATA box of promoters of eukaryotic protein-encoding genes transcribed by RNA polymerase II.

The promoter of the CD11b gene directs myeloid-specific and developmentally regulated expression

Human CD11b/CD18 (complement receptor type 3) is a member of the beta 2 integrin subfamily which also includes the heterodimers CD11a/CD18 and CD11c/CD18. The CD11 molecules and the common CD18 are the products of different genes that exhibit distinct though overlapping patterns of tissue- and developmental-specific expression. Whereas expression of CD11b and CD11c is almost exclusively restricted to cells of the myeloid lineage, that of CD11a and CD18 is panleukocytic. To begin to understand the mechanisms by which expression of these gene products is restricted to leukocytes and leukocyte subpopulations and to elucidate the mechanisms by which their expression is coordinated, we have cloned and characterized the promoter region of the CD11b gene. A single transcription initiation site has been identified and the region extending 242 base pairs upstream and 71 base pairs downstream of this site has been shown to be sufficient to direct tissue-, cell-, and development-specific expression in vitro, which mimics that of the CD11b gene in vivo. Within this region there are potential binding sites for transcription factors known to be involved in hematopoietic-specific and phorbol ester-inducible gene expression. Further analysis of this region of the CD11b gene and comparison with the promoters of the CD11a, CD11c, and CD18 genes should lead to significant insights into the molecular mechanisms by which these genes are regulated during hematopoietic development and upon activation.

Characterization of the promoter region of the human O6-methylguanine-DNA methyltransferase gene

O6-methylguanine-DNA methyltransferase (MGMT) is a ubiquitous protein responsible for repair of O6-alkylguanine, a mutagenic, carcinogenic and toxic lesion. To characterize the elements responsible for the regulation of the MGMT gene, a 2.6 kb Sstl fragment isolated from a genomic clone, was shown to contain 5' flanking sequences of the gene. The promoter activity of this fragment as well as various subfragments were tested in NIH 3T3 mouse fibroblasts by transient expression of the bacterial chloramphenicol acetyltransferase (CAT) gene linked to these fragments. Maximal promoter activity was observed in a 1.2 kb 3' terminal fragment, which contains the first untranslated exon. The transcription initiation site was identified in this fragment by primer extension and S1 mapping. Sequence analysis of this fragment showed the absence of TATA and CAAT boxes but an abundance of extremely GC-rich sequences, including ten GC hexanucleotide motifs 5'CCGCCC. Reduced CAT expression with the minimal promoter sequence suggests the presence of multiple regulatory elements.

Adult chicken alpha-globin gene expression in transfected QT6 quail cells: evidence for a negative regulatory element in the alpha D gene region

The chicken adult alpha-globin genes, alpha A and alpha D, are closely linked in chromosomal DNA and are coordinately expressed in vivo in an approximate 3:1 ratio, respectively. When subcloned DNAs containing one or the other gene are stably transfected into QT6 quail fibroblasts, the alpha A-globin gene is expressed at measurable RNA levels, but the alpha D gene is not. The alpha A gene expression can be considerably increased by the presence of a linked Rous sarcoma virus long terminal repeat enhancer, but that of the alpha D gene remains undetectable. Transfection with subclones containing both genes, either in cis or in trans, leads to considerably reduced alpha A RNA levels and still no observable alpha D gene expression. Transfection with deleted subclones suggests that maximal expression levels in this system require the alpha A-globin gene promoter, as opposed to that of the alpha D gene, but that such expression is greatly reduced by one or more DNA sequences which lie approximately 2,000 base pairs upstream of the alpha A gene, within the body of the alpha D gene.

Rat gastric H,K-ATPase beta-subunit gene: intron/exon organization, identification of multiple transcription initiation sites, and analysis of the 5'-flanking region

A rat genomic library was screened using a gastric H,K-ATPase beta-subunit cDNA probe, and two clones were identified. Restriction endonuclease mapping and Southern hybridization analyses indicated that each of these clones contains the entire H,K-ATPase beta-subunit gene. The nucleotide sequence was determined for the 8.75-kb transcription unit and 2.2 kb of the 5'-flanking region. The gene consists of seven exons and shows a high degree of similarity to the Na,K-ATPase beta 1-subunit gene. Primer extension and S1 nuclease protection analyses identified a major transcription initiation site 23 bases upstream of the translation start site and several minor transcription initiation sites located further upstream. The 5'-flanking region of the gene has two potential TATA sequences, each located 25-30 bases upstream of a transcription initiation site, and a number of potential promoter and regulatory elements. In addition, the 5'-flanking region contains nucleotide sequences that may regulate transcription through the formation of unusual DNA structures. These include a sequence that may form a triple helix and an adjacent sequence with the potential to form Z-DNA.

Differential ability of proximal and remote element pairs to cooperate in activating RNA polymerase II transcription

To investigate the synergism or cooperative interaction between transcription elements, we have designed and constructed a series of synthetic polymerase II promoters with different combinations of elements. These include three different CCAAT boxes, which correspond to the binding sites for CP1, CP2, and NFI, a GC box, a CACCC box, and an ATF/CREB-binding site. The synthetic promoters containing these elements in proximal positions were linked to a test gene (CAT). Tandem repeats of AP1- and AP2-binding sites, the simian virus 40 enhancer, and DNA-binding sites for GAL-estrogen receptor were cloned downstream of the test gene. The strength of these promoters was then tested in transient-expression assays in HeLa TK- cells. In the context of the adenovirus major late promoter TATA box, the promoters containing only certain combinations of elements are active in this assay. Some elements appear to cooperate nearly universally, but others exhibit strong selectivity. These results indicate strongly selective synergistic interactions between elements and suggest that levels of promoter strength may be determined by the extent of compatibility between factors bound to proximal and enhancer sites.

Differential ability of proximal and remote element pairs to cooperate in activating RNA polymerase II transcription

To investigate the synergism or cooperative interaction between transcription elements, we have designed and constructed a series of synthetic polymerase II promoters with different combinations of elements. These include three different CCAAT boxes, which correspond to the binding sites for CP1, CP2, and NFI, a GC box, a CACCC box, and an ATF/CREB-binding site. The synthetic promoters containing these elements in proximal positions were linked to a test gene (CAT). Tandem repeats of AP1- and AP2-binding sites, the simian virus 40 enhancer, and DNA-binding sites for GAL-estrogen receptor were cloned downstream of the test gene. The strength of these promoters was then tested in transient-expression assays in HeLa TK- cells. In the context of the adenovirus major late promoter TATA box, the promoters containing only certain combinations of elements are active in this assay. Some elements appear to cooperate nearly universally, but others exhibit strong selectivity. These results indicate strongly selective synergistic interactions between elements and suggest that levels of promoter strength may be determined by the extent of compatibility between factors bound to proximal and enhancer sites.

Analysis of the HSV-1 strain 17 DNA polymerase gene reveals the expression of four different classes of pol transcripts

We have investigated the structure and the expression of transcripts of the HSV-1 strain 17 DNA polymerase gene (pol) by various mapping methods including cDNA cloning. The majority of mature pol transcripts is strictly colinear with the pol gene. But additionally, pol cDNAs show a defined heterogeneity in respect to their 5'-terminal regions and can be divided into four classes with characteristic differences; (i) class 1 represents the major transcript (pol-R1) with initiation at HSV-1 positions 62,605-62,610, (ii) class 2 initiates about 70 bp downstream, (iii) class 3 is generated by splicing the short open reading frame (SORF) to a 5'-truncated part of the long open reading frame (LORF) which results in a partially different coding potential, and (iv) class 4 starts 120 bp upstream of the major initiation site in the central part of the origin of replication (oriL). S1 and Exo VII nuclease and RNase protection assays as well as primer extension analyses confirm the classification regarding the genuine structure of pol mRNAs and the differential usage of transcriptional start sites. Furthermore, the transcript classes can be distinguished from each other by their kinetics of appearance/disappearance in the cytoplasm: The first transcription of the pol gene is indicated by the predominant presence of class 2 and class 4 mRNAs at 2 hr postinfection (h.p.i.), followed by an increase of class 1 transcripts up to 4 h.p.i. and a parallel decrease of class 2 mRNAs. These data suggest that expression of the pol gene is finely regulated already at the transcriptional and/or posttranscriptional level prior to the translation of pol mRNAs.

H-2M3 encodes the MHC class I molecule presenting the maternally transmitted antigen of the mouse

Mta, the maternally transmitted antigen of mice, is a hydrophobic, N-formylated mitochondrial peptide, MTF, presented on the cell surface to cytotoxic T lymphocytes by a novel major histocompatibility complex class I molecule, encoded by H-2M3. We have cloned and sequenced two alleles of M3, which differ in their ability to present MTF despite greater than 99% identity in the coding regions. M3 is as divergent from classical, antigen-presenting H-2 molecules as from other class I genes of the Hmt and the Qa/Tla regions. Amino acids critical for folding of class I molecules are conserved in M3. Noncharged amino acids lining the peptide-binding groove and phenylalanine 171 may explain the unique interaction with MTF, and leucine 95 appears critical for immunological activity.

Organization of the gene for human erythrocyte membrane protein 4.2: structural similarities with the gene for the a subunit of factor XIII

Human erythrocyte band 4.2 is a major membrane-associated protein with an important, but still undefined, role in erythrocyte survival. We previously sequenced the complete cDNA for band 4.2 and showed that the protein has a strong sequence identity with the transglutaminase family of proteins but lacks transglutaminase activity. Here we have analyzed the genomic organization of band 4.2. The band 4.2 gene is approximately 20 kilobases, consisting of 13 exons and 12 introns. Reticulocytes contain two different sized messages for band 4.2, and our results show that the major, smaller, message is produced by alternative splicing within band 4.2 exon I. The upstream region of the gene has several prospective promoter elements arranged in a pattern similar to that of two other erythroid genes, beta-globin and porphobilinogen deaminase. Alignment of the band 4.2 amino acid sequence with that of the a subunit of human coagulation factor XIII and division of the sequences into exons reveal a remarkable correspondence, and in most cases identity, in the sizes of the paired exons. Moreover, each corresponding intron of the two genes is of an identical splice junction class. These and other similarities suggest that the gene for band 4.2 is closely related to and possibly derived from that for the a subunit of factor XIII and that the proteins may share common structural and functional properties.

Transcriptional role of a conserved GATA-1 site in the human epsilon-globin gene promoter

The epsilon-globin gene is the first of the human beta-like globin genes to be expressed during development. We have analyzed protein-DNA interactions in the epsilon-globin promoter region by DNase I footprinting and electrophoretic mobility shift experiments using nuclear extracts from K562 human erythroid cells and from nonerythroid HeLa cells. A restricted set of ubiquitous proteins, including Sp1, bound to regions of the promoter including the CACCC and CCAAT sites. Three interactions, at positions -213, -165, and +3 relative to the transcription start site, were erythroid specific and corresponded to binding of GATA-1, a transcription factor highly restricted to the erythroid lineage. Interestingly, the GATA-1 site at -165 has been conserved in the promoters of 10 mammalian embryonic globin genes. Point mutations demonstrate that GATA-1 binding to this site is necessary for interaction with an erythroid-specific enhancer but that in the absence of an enhancer, GATA-1 does not increase transcription.

Structure and expression of the negative growth factor mouse beta-galactoside binding protein gene

Following the identification of murine beta-galactoside binding protein (mGBP) as an autocrine negative growth factor we have now isolated and characterized the genomic region spanning the mGBP gene and have determined the 5' end of the transcript by primer extension, S1 mapping and mRNA sequence. The gene is found to be contained within 4 kilobases and composed of four exons of 79, 80, 171 and 197 nucleotides separated by three introns of 1200, 1600 and 193 nucleotides. The DNA region upstream of the 5' end of the transcript contains canonical sequences for eukaryotic promoter elements including CAT and TATA boxes and several DNA motifs for potential transcription regulation. The gene is differentially expressed in a variety of normal tissues.

Characterization of the human argininosuccinate lyase gene and analysis of exon skipping

A cosmid clone containing the entire human argininosuccinate lyase gene was isolated and characterized. The gene is approximately 35 kb in length and is divided into 16 exons. The sequence surrounding all splice sites was determined, and one unusual 5' splice site sequence in which a GC dinucleotide occurred instead of the consensus GT dinucleotide was observed. The exon structure of the gene is identical to that of the rat and similar to that of the delta-crystallin genes in the chicken. The transcription initiation site was identified, and 252 bases 5' of that site were sequenced. Within that region, the GC content is 75%, no TATA element was observed, and multiple potential Spl and CACCC binding sites were noted. Also, a putative consensus sequence that may play a role in the regulation of urea cycle genes was identified within this region. Analysis of the structure of the mature mRNA derived from this gene revealed that the sequences encoded by exon seven were deleted in approximately 5-10% of the mature mRNA in all tissue sources examined.

Transcriptional role of a conserved GATA-1 site in the human epsilon-globin gene promoter

The epsilon-globin gene is the first of the human beta-like globin genes to be expressed during development. We have analyzed protein-DNA interactions in the epsilon-globin promoter region by DNase I footprinting and electrophoretic mobility shift experiments using nuclear extracts from K562 human erythroid cells and from nonerythroid HeLa cells. A restricted set of ubiquitous proteins, including Sp1, bound to regions of the promoter including the CACCC and CCAAT sites. Three interactions, at positions -213, -165, and +3 relative to the transcription start site, were erythroid specific and corresponded to binding of GATA-1, a transcription factor highly restricted to the erythroid lineage. Interestingly, the GATA-1 site at -165 has been conserved in the promoters of 10 mammalian embryonic globin genes. Point mutations demonstrate that GATA-1 binding to this site is necessary for interaction with an erythroid-specific enhancer but that in the absence of an enhancer, GATA-1 does not increase transcription.

Characterization of the promoter for the rat and human link protein gene

We have isolated the 5'-end of the gene for the rat and human link protein by screening genomic libraries with oligonucleotides corresponding to the 5'-cDNA sequence. Several overlapping clones were isolated for the human link protein gene, while only one clone was obtained for the rat. All the clones contained a single exon of which the sequence was identical to the most 5'-end of the rat and human cDNAs. Transcription initiation sites for the rat link gene were identified by primer extension and S1 protection analysis using total RNA from the rat Swarm chondrosarcoma. Transcriptional initiation sites for the human link gene were determined by specific primer extension of RNA from human fetal cartilage. Comparison of 1500 bp of 5'-flanking sequence between the rat and human link protein genes showed strong sequence conservation near the start site of transcription with 80% overall identity. Analysis of the 5'-flanking regions also revealed a large inverted repeat consisting of repeating purine-pyrimidine, which has the potential to form left-handed Z-DNA. Transcriptional regulation of the link protein gene was studied by coupling either 7.0 kb or 0.85 kb of 5'-flanking rat DNA to the chloramphenicol acetyltransferase (CAT) gene followed by transfection into chick embryonic chondrocytes (CEC) and HeLa cells. Both constructs had considerable CAT activity in CEC cells and less activity in HeLa cells. Furthermore, inclusion of a DNA fragment from the first intron increased relative CAT activity in both of these cell types. The increased activity from the first intron was shown to be orientation independent in CEC. These results indicate the presence of positive cisacting regulatory elements in both the promoter and first intron of the rat gene for link protein.