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Results for “Alternative Splicing”

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PubMed1994

Functional differences among alternatively spliced variants of Slowpoke, a Drosophila calcium-activated potassium channel.

The Slowpoke locus of Drosophila melanogaster encodes a family of alternatively spliced mRNAs which encode large conductance calcium-activated potassium channels. Variability residues in blocks of amino acids designated boxes A, C, E, G, and I. Oocytes were injected with cRNAs that had been chosen for direct functional comparison of single box differences. Single channel records from inside-out patches of oocyte membranes expressing A1 or A3 forms, E1 or E2 forms, and G2-G5 forms were analyzed and compared. The main functional difference between A1 and A3 was in unitary conductance, whereas the main difference in properties between E1 and E2 was in calcium sensitivity. Activation kinetics were different between G3 and G5, but not consistently in different A and E box backgrounds. The results indicate that alternative splicing of a common RNA precursor contributes to the functional diversity of the expressed channel. Our findings suggest that the variable region of the Slowpoke channel subunit comprises modular, yet interactive functional domains which influence the essential features of unit conductance, calcium sensitivity, and gating.

Alternative Splicing↗

PubMed1999

Identification of 4 different alternatively spliced HLA-A transcripts.

During the development of a sequencing based typing (polymerase chain reaction (PCR)-SBT) protocol for the HLA-A locus, the presence of two bands in addition to the expected full-length product were observed in the template generating PCR in some of the samples investigated. Despite a profound optimisation of the PCR, these new products of lower molecular weight remained present. The new products were not associated with specific alleles. However, the affected samples consisted of peripheral blood lymphocytes isolated from four patients with colorectal cancer, one patient diagnosed with myeloma, and a colon tumor cell line. In order to elucidate the nature of this phenomenon, a number of these products were cloned and sequenced. Sequence analysis revealed that alternative splicing of the HLA-A transcript was responsible for the generation of these smaller products. Thus, a number of clones were generated from transcripts in which a 276 base pair region corresponding exactly to exon 3 had been spliced out. Three additional transcripts lacking exons 2 and 3, exons 3 and 4, and transcripts lacking exons 2-4 respectively, were identified as well. These results are in some respects similar to observations made for HLA-G, one of the nonclassical class I loci, in which a number of alternatively spliced transcripts have been identified. However, no specific functions have been ascribed to these molecules nor have the truncated proteins encoded by these transcripts been identified, thereby questioning the biological significance of these observations. Nevertheless, our findings indicate that alternative splicing of the HLA-A transcript may take place to a small extent in virtually all cells, and it is possible that their generation promote escape from immune surveillance.

Alternative Splicing↗

PubMed2004

Identification and expression analysis of an IL-18 homologue and its alternatively spliced form in rainbow trout (Oncorhynchus mykiss).

A homologue of interleukin 18 has been identified from rainbow trout, Oncorhynchus mykiss. The trout IL-18 gene spans 3.7 kb and consists of six exons and five introns, sharing the same gene organization with its human counterpart. The putative translated protein is 199 amino acids in length with no predicted signal peptide. Analysis of the multiple sequence alignment reveals a conserved ICE cut site, resulting in a mature peptide of 162 amino acids. The trout IL-18 shares 41-45% similarity with known IL-18 molecules and contains an IL-1 family signature motif. It is constitutively expressed in a wide range of tissues including brain, gill, gut, heart, kidney, liver, muscle, skin and spleen. Transcription is not modulated by lipopolysaccharide, poly(I:C) or trout recombinant IL-1beta in primary head kidney leucocyte cultures and RTS-11 cells, a macrophage cell line. However, expression is downregulated by lipopolysaccharide and rIL-1beta in RTG-2 cells, a fibroblast-like cell line. An alternatively spliced form of IL-18 mRNA has also been found and translates into a 182 amino acid protein with a 17 amino acid deletion in the precursor region of the authentic form. This alternatively spliced form is also widely expressed although much lower than the authentic form. Interestingly, its expression is upregulated by lipopolysaccharide and poly(I:C), but is not affected by rIL-1beta in RTG-2 cells. The present study suggests that alternative splicing may play an important role in regulating IL-18 activities in rainbow trout.

Alternative Splicing↗

PubMed1991

The vascular endothelial growth factor family: identification of a fourth molecular species and characterization of alternative splicing of RNA.

Vascular endothelial growth factor (VEGF) was recently identified as a secreted, direct-acting mitogen specific for vascular endothelial cells and capable of stimulating angiogenesis in vivo. Molecular cloning revealed multiple forms of VEGF, apparently arising from alternative splicing of its RNA transcript. We have examined various human cDNA libraries by the polymerase chain reaction technique and discovered a fourth molecular form, VEGF206. This form contains a 41-amino acid insertion relative to the most abundant form, VEGF165, and includes the highly basic 24-amino acid insertion found in VEGF189. Southern blot analysis revealed that a single gene encoded these various forms, and nucleic acid sequence analysis of a portion of the VEGF gene revealed an intron/exon structure compatible with alternative splicing of RNA as a mechanism for their generation. Transient transfection of human embryonic kidney 293 cells showed that, like VEGF189, VEGF206 was predominately cell-associated and only very poorly secreted despite the presence of the signal peptide identical to that found in VEGF121 and VEGF165, both of which are efficiently exported from the cell. Vascular permeability activity was detected in the medium of 293 cells transfected with all four forms of VEGF; however, endothelial cell mitogenic activity was apparent only with VEGF121 and VEGF165. Thus, alternative splicing of VEGF RNA can produce four polypeptides with strikingly different secretion patterns, which suggests multiple physiological roles for this family of proteins.

Amino Acid Sequence↗

PubMed1997

Selective regulation of agrin mRNA induction and alternative splicing in PC12 cells by Ras-dependent actions of nerve growth factor.

The extracellular matrix protein agrin plays an important role in the formation and maintenance of the neuromuscular junction. However, regulation of agrin gene expression and pre-mRNA splicing, important in determining the biological actions of agrin, is not well understood. To begin to identify mechanisms controlling agrin expression, quantitative polymerase chain reaction techniques were used to analyze the effect of growth factors on the expression of agrin mRNA isoforms in rat pheochromocytoma (PC12) cells. Agrin transcripts in untreated cells lacked inserts in the Y and Z sites (agriny0z0), encoding agrin isoforms with low acetylcholine receptor aggregating activity and a primarily non-neuronal tissue distribution. Transcripts encoding isoforms with high aggregating activity and neuronal tissue distribution (agriny4z8, agriny4z11, and agriny4z19) were not detected. Treatment of PC12 cells with nerve growth factor (NGF) caused a significant increase in total agrin mRNA. In contrast, exposure to epidermal growth factor had no effect. Analysis of alternative splicing of agrin mRNA revealed that NGF elicited a specific increase in agriny4 and agrinz8 mRNAs that did not occur in the presence of epidermal growth factor, insulin, dexamethasone, or retinoic acid. Analysis of PC12 sublines stably overexpressing a dominant inhibitory form of p21 Ras indicated that NGF induced changes in levels of agrin mRNA and alternative splicing required Ras activity. The results show that NGF can influence important aspects of neuronal differentiation by regulating alternative splicing. Furthermore, these data provide insight into the mechanisms governing agrin gene expression and suggest that neurotrophic factors may play a role in regulating agrin expression in vivo.

Agrin↗

PubMed1995

Products of alternatively spliced transcripts of the Wilms' tumor suppressor gene, wt1, have altered DNA binding specificity and regulate transcription in different ways.

The Wilms' tumor susceptibility gene, wt1, encodes a transcription factor of the zinc finger protein family. Mutations in the WT1 gene product have been detected in both sporadic and familial Wilms' tumors, suggesting that alterations in WT1 may disrupt its normal function as a transcriptional regulator. The transcripts of wt1 are alternatively spliced; however, roles of the alternatively spliced forms have not been defined. The major transcript of wt1 encodes a WT1 protein [WT1(+KTS)+17AA] that contains three amino acids (+KTS) between the third and fourth zinc fingers and a serine-rich, 17 amino acid (+17AA) domain N-terminal to the zinc finger region. We now show that the WT1 (+KTS) forms functionally bind to a unique G+C-rich sequence within the PDGF A-chain promoter. We also show that WT1 (+KTS)+17AA functions as a strong transcriptional repressor and that +17AA alone fused to the zinc-finger domain of WT1 or to the heterologous DNA binding domain of GAL4 functions independently as a repressor. Deletion of four serine residues within +17AA abolishes the repressor activity of +17AA. These results indicate that wt1 products with +17AA contain an additional dominant repressor domain and that the presence or absence of +KTS determines alternative DNA binding specificity.

3T3 Cells↗

PubMed2000

Bovine NAD+-dependent isocitrate dehydrogenase: alternative splicing and tissue-dependent expression of subunit 1.

NAD+-dependent isocitrate dehydrogenase (IDH), a key regulatory enzyme in the Krebs cycle, is a multi-tetrameric enzyme. At least three of the subunits in the core tetramer of mammals are unique gene products. Subunits 1/beta and 2/gamma are considered to be regulatory, while subunits 3,4/alpha, comprising half the tetramer, are catalytic. The full sequence was obtained for the major subunit 1 cDNA in bovine heart, IDH 1-A. A second cDNA, rare in heart, was also identified (IDH 1-B). Differences in the two were confined to the 3'-region, suggesting alternative splicing. Screening of brain, kidney, and liver RNA showed the presence of IDH 1-A and 1-B and a third major species, IDH 1-C. Amplification of bovine genomic DNA by PCR across the regions of difference produced a single product. Comparison of the genomic and mRNA sequences showed that IDH 1-A resulted from splicing of exon W to exon Y, eliminating intron w, exon X, and intron x. IDH 1-B was formed by splice junctions between exon W, exon X, and exon Y. IDH 1-C resulted from splicing of exon W to exon X and subsequent retention of intron x. The 2 proteins predicted from these 3 mRNAs are identical over their first 357 residues. Protein IDH 1-A, resulting from a termination codon within exon Y, contains an additional 26 residues. Proteins IDH 1-B and 1-C derive from a common termination codon within exon X and contain an additional 28 residues. The two C-terminal regions differ notably in the number and nature of charged residues, resulting in proteins with a charge difference of 3.2 at pH 7.0. Subunit 1 sequences previously reported from other species grouped with one or the other of the bovine proteins. No evidence was found for alternative splicing in subunit 3,4/alpha. The results of the present study, together with recent work on the 2/gamma subunit [Brenner,V., Nyakatura, G., Rosenthal, A., and Platzer, M. (1998) Genomics 44, 8], indicate that the regulatory subunits of the enzyme, but not the catalytic, possess alternatively spliced forms varying in C-terminal properties with tissue-specific expression. The finding is suggestive of a mechanism for modulation of allosteric regulation tailored to the needs of different tissues.

Alternative Splicing↗

PubMed2005

A quantitative method for comparison of expression of alternatively spliced genes using different primer pairs.

In this paper we describe a novel two-step method for comparison of expression of alternatively spliced genes by quantitative PCR (QPCR) applying different primer pairs. As a model system we used rat decay accelerating factor (DAF; CD55) mRNA, which comprises three different isoforms: soluble (sDAF), transmembrane (tmDAF) and glycosyl-phosphatidylinositol (GPI) anchored (gpiDAF) forms. The first step was to prepare solid phase specific for each mRNA isoform and purify the three DAF-forms from total RNA. We then assessed amplification efficiency of primer pairs designed to recognise each of the isoforms using equimolar amounts of the three purified DAF mRNAs. The final step in our assay was to compare expression of the three DAF-isoforms in testis by QPCR taking into account the efficiency of their amplification to enable quantification. The RNA capture/QPCR method we described here can be used for quantifying the expression ratios of alternatively spliced mRNAs from a single gene or for direct comparison of expression of different genes.

Alternative Splicing↗

PubMed2006

Alternative splicing of delta-like 1 homolog (DLK1) in the pig and human.

Delta-like homolog 1 (DLK1), a paternally imprinted gene with several alternative splicing isoforms, is an important regulator of fetal and postnatal development. We report the sequence of porcine DLK1 (pDLK1) and examine the expression and alternative splicing isoforms in the pig (Sus scrofa) and human. DLK1-A was the sole isoform identified in human tissues and has been shown to be present in mouse and cattle. Surprisingly, DLK1-A was undetected in various tissues from fetal and postnatal pigs. Instead, DLK1-C2 was the most abundant isoform while DLK1-B was expressed to a lesser extent. In fractionated adipose tissue, pDLK1 was most highly expressed in the stromal-vascular cell fraction. In addition, total pDLK1 was highly expressed in fetal adipose tissue but dramatically decreased postnatally. Our data suggests that expression of DLK1-B and -C2 isoforms is sufficient for normal pig development. Furthermore, human and pig samples showed no alterations in species-specific splicing, but expression levels decreased with age, suggesting that regulation of expression, not splicing, is the most likely mechanism controlling the biological function of DLK1.

Adipocytes↗

PubMed1995

An alternatively spliced exon in the extracellular domain of the human alpha 6 integrin subunit--functional analysis of the alpha 6 integrin variants.

Variants in the extracellular domain of the integrin alpha 7 subunit which arise as a consequence of alternative splicing of mRNA have recently been reported. Two alternative exons, X1 and X2, have been identified in the alpha 7 gene, and homologous exons were found for alpha 6 (Ziober et al., 1993). In this study, we have isolated the region of the alpha 6 gene containing exons X1 and X2 that are, like those of alpha 7, located between stretches of DNA that encode the homologous repeat domains III and IV, proximal to the three divalent cation binding sites of the alpha 6 subunit. We demonstrated by reverse transcriptase polymerase chain reactions and confirmed by sequencing that alpha 6X1 and alpha 6X1X2 mRNAs are generated by alternative splicing of exon X2. The alpha 6X1X2 mRNA is expressed in a limited number of tissues and cell lines and it is always co-expressed with the ubiquitous alpha 6X1 mRNA. Stable transfection of K562 cells with full length cDNAs for the alpha 6AX1X2 and beta 4 subunits resulted in cell populations that expressed the alpha 6AX1X2 variant, in association with either beta 1 or beta 4, on their surface. In addition, a population of cells was isolated that expressed the alpha 6AX1X2 variant at low levels and almost exclusively in association with beta 1. Comparison of the alpha 6AX1X2 integrins with alpha 6AX1 using similarly transfected cells showed no obvious differences between the alternative extracellular alpha 6A isoforms with respect to ligand specificity and activation-dependency of ligand binding. After treatment with the anti-beta 1 stimulatory antibody TS2/16, both the alpha 6AX1 beta 1 and alpha 6AX1X2 beta 1 integrin variants mediated cell adhesion to EHS tumor laminin (laminin-1), kalinin (laminin-5), human placental (laminin-2 and -4) and bovine kidney laminins. In contrast, the alpha 6AX1 beta 4 and alpha 6AX1X2 beta 4 integrins also mediated cell adhesion to laminin and kalinin without stimulation. Furthermore, the different transfectants did not differ in their ability to spread on kalinin. The presented data indicate that the X2 region in alpha 6 is not involved in defining ligand specificity or affinity.

Alternative Splicing↗

PubMed2001

mARVCF cellular localisation and binding to cadherins is influenced by the cellular context but not by alternative splicing.

ARVCF, a member of the catenin family, is thought to contribute to the morphoregulatory function of the cadherin-catenin complex. Recently, we reported the isolation and characterisation of murine ARVCF (mARVCF), particularly its interaction with M-cadherin. Here, we describe the identification of novel mARVCF isoforms that arise by alternative splicing. At the N-terminus, alternative splicing results in the inclusion or omission of a coiled-coil region probably important for protein-protein interactions. At the C-terminus, four isoforms also differ by domains potentially important for selective protein-protein interaction. The eight putative mARVCF isoforms were expressed as EGFP-fusion proteins in six different cell lines that exhibit a distinct pattern of cadherins. Apparently, binding of the mARVCF isoforms to M-, N-, or E-cadherin is generally unaffected by their altered N- and C-termini, as revealed by the MOM recruitment assay. However, mARVCF isoforms reproducibly exhibit differential localisation in distinct cellular environments. For example, mARVCF isoforms are unable to colocalise with N-cadherin in EJ28 carcinoma cells but do so in HeLa cells. Our results suggest that the subcellular localisation of mARVCF may be determined not only by the presence or absence of an appropriate interaction partner, in this case cadherins, but also by the cellular context.

Alternative Splicing↗

PubMed2006

Anti-Müllerian hormone (AMH/AMH) in the European sea bass: its gene structure, regulatory elements, and the expression of alternatively-spliced isoforms.

In mammals, a multitude of studies have shown that anti-Müllerian hormone (AMH/AMH), apart from inducing Müllerian duct regression during male sexual differentiation, exerts inhibitory effects on male and female gonadal steroidogenesis and differentiation. However, in lower vertebrates like teleost fish, the function of AMH/AMH has been far less explored. As a first step to unravel its potential role in reproduction in teleost fish, we isolated and characterised the AMH gene in the European sea bass (sb), Dicentrachus labrax, determined putative regulatory elements of its 5'-flanking region, and analysed its gene expression and those of alternatively-spliced transcripts. The characterisation of sb-AMH revealed distinct features that distinguishes it from mammalian and bird AMH, suggesting a high rate of diversification of AMH during vertebrate evolution. It contained 7 exons that were divided by 6 introns, of which the last intron (intron vi) was localised only a few nucleotides upstream of the putative peptide cleavage site. The guanine and cytosine content of the open reading frame (ORF) was 52.7% and thus notably lower than that of bird and mammalian AMH. Sb-AMH cDNA was 2045 base pairs (bp) long, containing an ORF of 1599 bp encoding 533 amino acids. Deduced amino acid similarities of the conserved, carboxyterminal domain were highest with AMH in Japanese flounder (84.2%) and lowest with chicken AMH (45.5%). In the proximal promoter sequence of sb-AMH, a steroidogenic factor-1 (SF-1) binding site was present; however other regulatory sequences essential for transcriptional activation of AMH in mammals were absent. Likewise, there was no sequence homology to an SF3A2 sequence within the first 3200 bp upstream of the sb-AMH translation start site. Gene expression of sb-AMH and of alternatively-spliced sb-AMH transcripts were analysed in male and female juvenile and adult gonads as well as in somatic tissues of juvenile males. sb-AMH expression was highest in juvenile testis, but still remarkably high in juvenile ovaries and adult testis, as well as in brain, pituitary, and heart of juvenile male sea bass. Apart from adult ovary, levels of alternatively-spliced sb-AMHexonII/-99 were marginal in comparison with sb-AMH. In contrast, the transcript variant sb-AMHexonVII/+5 was expressed to a similar extent as sb-AMH in all tissues examined. The results of this work have provided the basis for future studies concerning the regulation and function of AMH/AMH in this species.

5' Flanking Region↗

PubMed1995

Molecular cloning of a cDNA for the human inositol 1,4,5-trisphosphate receptor type 1, and the identification of a third alternatively spliced variant.

The Inositol 1,4,5-trisphosphate receptor (IP3R) is an intracellular calcium channel involved in coupling cell membrane receptors to calcium signal transduction pathways within the cell. We have cloned a cDNA for the human type 1 inositol 1,4,5-trisphosphate receptor. The sequence contains the S2 splice site which appears to be the region most divergent between rat and human. We now report an additional alternatively spliced region in the coupling domain, that is 9 amino acids long, which we term S3. Alternatively spliced forms are found in both human and rat. PCR analysis of brain and peripheral tissues from human and rat shows both transcripts of the type 1 inositol 1,4,5-trisphosphate receptor in all tissues. The long form predominates in most brain regions (except the cerebellum) while the short form predominates in peripheral tissues. The sequence of the longer form in human appears to create an additional consensus protein kinase C phosphorylation site.

Alternative Splicing↗

PubMed1986

Structural and functional analysis of an alternatively spliced chicken TK messenger RNA.

The nucleotide sequence of independent cDNA clones revealed that TK transcripts can undergo alternative splicing within the 3' nontranslated portion of the message. The most abundant mRNA is 2.1 kb in length and is colinear with the underlying genomic sequence for at least the first 1052 bases of its 3' nontranslated region. A less abundant mRNA, 1.3 kb in length, differs from the larger mRNA in that an 863 base intron is spliced from the 3' nontranslated region. The possibility that removal of the alternatively spliced intron allows the small mRNA to persist in postreplicative cells was investigated in two ways. First, the levels of large and small TK mRNA in tissues expressing differential growth rates was determined. Second, the pattern of TK enzyme expression during differentiation was analyzed in muscle cells transformed with recombinant TK genes lacking the 3' nontranslated intron. Both lines of experimentation indicated that the small TK mRNA was as dependent as the large TK mRNA on the replicative state of the cell.

Animals↗

PubMed1992

Hypertension induces alternatively spliced forms of fibronectin in rat aorta.

Fibronectin expression was shown recently to increase in the rat aorta in response to experimental hypertension. Fibronectin is known to alter the phenotype of vascular smooth muscle and endothelial cells, and relative changes in the expression of different isoforms of fibronectin, generated by alternative splicing and distinguished by the absence or presence of inserts designated as EIIIA, EIIIB, and V, may reflect a change in cell phenotype. In the present study we examined the expression of alternatively spliced forms of aortic fibronectin during deoxycorticosterone-salt hypertension. Aortic RNA was analyzed quantitatively using Northern blot analysis and ribonuclease protection assays. Using Northern blot analysis, deoxycorticosterone-salt treatment for 21 days led to a 4.9-fold increase in EIIIA fibronectin messenger RNA, while EIIIB and V forms increased by 2.6- and 2.5-fold, respectively. As determined by ribonuclease protection assays, the percentage of fibronectin transcripts containing either EIIIA, EIIIB, or V in control aorta was 7.3%, 19%, and 40%, respectively. The percentage of EIIIA transcripts increased 42% over control levels after 21 days of deoxycorticosterone-salt treatment, whereas no proportionate change in the other alternatively spliced forms was found. Thus, all forms increased, but a selective increase in the EIIIA form was induced. Analogous increases in each of the fibronectin isoforms were found in the spontaneously hypertensive rats when compared with age-matched Wistar-Kyoto or Wistar rats, and 40-week-old animals showed increases over 10-week-old animals in all strains, consistent with an age-dependent increase in aortic fibronectin expression.

Animals↗

PubMed2002

Dual regulation of telomerase activity through c-Myc-dependent inhibition and alternative splicing of hTERT.

Telomerase is believed to be induced upon proliferation and inhibited when cells differentiate. Thus, regulation of telomerase activity could be an important mechanism to limit growth of normal and cancer cells. Using transforming growth factor-beta 1 (TGF-beta1), which is known to control proliferation in epithelial cells, we now demonstrate that in the human HaCaT skin keratinocytes, TGF-beta1 downregulated c-Myc, and this blocked proliferation. This also caused a decrease in hTERT expression, which in turn inhibited telomerase activity. Overexpressing hTERT recovered telomerase activity but not proliferation, whereas constitutive expression of c-Myc recovered proliferation and hTERT expression. Nevertheless, telomerase remained inhibited, thus dissociating proliferation and telomerase activity. In addition, we show that TGF-beta1 inhibited telomerase activity despite ongoing hTERT transcription by inducing loss of the full-length hTERT transcript (mediating telomerase activity) and retaining high expression of the inactive beta variant. These changes in the splicing pattern reversed upon TGF-beta1 removal, as did inhibition of telomerase activity, suggesting that alternative splicing may represent a novel mechanism of telomerase regulation by TGF-beta1. In addition, we show that destruction of tissue integrity (in a model for epidermal blistering) resulted in a rapid induction of the inactive beta variant, whereas tissue regeneration (formation of a stratified epithelium) correlated with a shift to the active full-length transcript, which is the dominant form in intact epidermis. Thus alternative splicing may not be restricted to TGF-beta1 but may add a more general mechanism of hTERT regulation in epidermal cells.

Alternative Splicing↗

PubMed1995

T cell receptor iota an alternatively spliced product of the T cell receptor zeta gene.

It has been previously suggested that three alternative splicings of the murine T cell receptor (TCR) zeta gene are involved in the regulation of TCR/CD3 transduction signals. We here describe a new alternative splicing of this gene (TCR iota), cloned by reverse transcriptase-polymerase chain reaction, that is encoded by exons 1-7 and 10. The protein putatively encoded by TCR iota mRNA differs in its carboxy terminus from that coded by TCR0 as a consequence of the reading frame shift of exon 10. The possible role of this new splicing in TCR modulation is briefly discussed.

Amino Acid Sequence↗

PubMed1990

Alternative splicing of the human c-myb gene.

Two cDNA clones of the human c-myb gene have been isolated from a CCRF-CEM leukemia cell cDNA library and sequenced in their entirety. These sequences, when compared with those previously reported for the human c-myb gene, reveal an alternative splicing process that generates at least four forms of the c-myb message. Three of these forms co-migrate on Northern blots and are co-expressed in several human hematopoietic cell types. Data on sequence comparisons with mouse and chicken homologues of c-myb coupled with oligonucleotide hybridization to genomic clones of the human c-myb gene indicate that this alternative splicing process utilizes three closely spaced splice donor sites and two unique exons present between viral defined exons 5 and 6. In one clone, the alternative splicing would generate a predicted myb protein with a three amino acid deletion in the region involved in transcription activation. In the other clone, incorporation of a new exon leads to introduction of a translation stop codon leading to loss of the entire carboxy terminus of the protein. This includes loss of a portion of the region involved in transcription activation as well as a separate highly conserved domain. The effect of these changes on protein function is currently unknown.

Base Sequence↗