Conserved alternative splicing in the 5'-untranslated region of the muscle-specific enolase gene. Primary structure of mRNAs, expression and influence of secondary structure on the translation efficiency

Diversity in transcriptional start site selection and alternative splicing affects the 5'-UTR of mouse striated muscle myosin transcripts

We have analyzed nearly 2,000 myosin heavy chain gene (Myh) clones representing over 30 different transcripts from seven of eight striated muscle Myh genes expressed in mouse. We also report the transcriptional start sites (TSS) for the mouse developmental Myh genes. The data reveal a previously unknown diversity of TSSs and 5'-end alternative splicing in these transcripts. The cardiac Myh6 gene had two major TSSs. Use of the major downstream site led to an alternatively spliced second exon. Each of the other Myh genes had one major TATA-directed TSS and one or more minor alternative TSSs, some associated with alternative splicing. The minor transcripts were associated with polysomes and their spatial-temporal expression largely mirrored that of the major transcripts in wild-type, Myh1 null, Myh4 null, injured, and uninjured muscle, except that one form of Myh7, detected in heart, was not detected in diaphragm, and the ratio of the two major Myh6 transcripts varied in some circumstances. These findings indicate that alternative TSS usage and alternative splicing in the 5'-UTR are a general feature of murine Myh gene expression and that Myh gene regulation is more complex than previously appreciated.

Cloning, expression and mutagenesis of a subunit contact of rabbit muscle-specific (betabeta) enolase

The cDNA for rabbit muscle-specific (betabeta) enolase was cloned, sequenced and expressed in Escherichia coli. This betabeta-enolase differs at eight positions from that sequenced by Chin (17). Site-directed mutagenesis was used to change residue 414 from glutamate to leucine, thereby abolishing a salt bridge involved in subunit contacts. Recombinant wild-type and mutant enolase were purified from E. coli and compared to enolase isolated from rabbit muscle. Molecular weights were determined by mass spectrometry. All three betabeta-enolases had similar kinetics, and UV and circular dichroism (CD) spectra. The mutant enolase was far more sensitive to inactivation by pressure, by KCl or EDTA, and by sodium perchlorate. We confirmed, by analytical ultracentrifugation, that the sodium perchlorate inactivation was due to dissociation. DeltaG(o) for dissociation of enolase was decreased from 49.7 kJ/mol for the wild-type enzyme to 42.3 kJ/mol for the mutant. In contrast to the wild-type enzyme, perchlorate inactivation of E414L was accompanied by a small loss of secondary structure.

Protein tyrosine phosphatase (PC12, Br7,S1) family: expression characterization in the adult human and mouse

Protein tyrosine phosphatases (PTPs) play important roles in modulating signals transduced by tyrosine kinases. Certain phosphatases have been implicated as having important roles in embryonic development as well as in adult physiology. Although both kinases and phosphatases are equally important in regulating signal transduction, phosphatases as a group have not been well characterized. Thus, characterization of sequence, expression, and biological function for additional phosphatases is informative. PTPBr7/PC12 and PTPSl are mouse receptor PTPs sharing similar amino acid sequences. Northern blot analysis demonstrated expression of these genes in adult rodent brain and revealed previously uncharacterized transcripts in the brain and other tissues. Our results demonstrate that PTPBr7/PC12 and PTPSl are members of a larger family of PTPs. We have identified two novel family members as well as several novel transcriptional splice variants from both human and mouse colon cDNA libraries. Expression analysis demonstrated that the various mRNA transcripts are differentially expressed, with the highest levels found in the brain, intestinal tract, uterus, and placenta. In situ hybridization analysis of mouse brain and intestinal tissues established that each isoform has a unique expression pattern in specific cell populations as well as in tissue regions. Furthermore, these restricted patterns suggest that the encoded family of phosphatases may play roles in modulating signal transduction pathways important for specific cell types and biological processes.

A new exon in the 5' untranslated region of the connexin32 gene

The cloning and sequencing of two bovine connexin32 cDNAs are reported. Comparative analysis with known corresponding mammalian cDNA and protein sequences, besides confirming a high degree of similarity among these proteins, allowed us to identify some specific features of the bovine connexin32 gene. The latter include: the presence of a novel exon in the 5' UTR which is alternatively spliced, giving rise to a new mRNA species; the presence of two potential hairpin loops in the 5' and 3' UTR; and the presence of an additional amino acid, glycine235, in the C-terminal domain of the 284 residue protein. Among the common features, the presence of polypyrimidine clusters within the 3' UTR, containing a consensus sequence for a cis-acting element, is noteworthy. Expression of connexin32 mRNAs was analysed in 16 bovine tissues. Transcript analysis suggests the presence, in cattle, of an alternative downstream promoter.

Characterization of a splice variant of metastasis-associated h-mts1 (S100A4) gene expressed in human infiltrating carcinomas of the breast

The h-mts1 (S100A4) is a member of the S100 gene family, coding for a calcium-binding protein. It is a metastasis-associated gene whose expression shows strong correlation with the proliferative potential and invasive and metastatic ability of cancers. In a proportion of human intraductal carcinomas of the breast, a shorter variant h-mts1 transcript (h-mts1v) of approximately 450 nucleotides is expressed. We have characterized the transcript using reverse transcriptase-polymerase chain reaction employing exon-specific oligonucleotides. We show here that the noncoding exon 1a/1b is lost in the variant cDNA. Exons 2 and 3, which code for the protein, seem to be present in the variant isoform. The RT-PCR products obtained using exons 2- and 3-specific oligonucleotides showed a high degree of sequence homology with exons 2 and 3 of the h-mts1 gene. The expression of the variant transcript could be influencing disease progression, albeit not as effectively as the normal unspliced h-mts1 transcript.

Biochemical characterization of the mouse muscle-specific enolase: developmental changes in electrophoretic variants and selective binding to other proteins

The glycolytic enzyme enolase (EC 4.2.1.11) is active as dimers formed from three subunits encoded by different genes. The embryonic alphaalpha isoform remains distributed in many adult cell types, whereas a transition towards betabeta and gammagamma isoforms occurs in striated muscle cells and neurons respectively. It is not understood why enolase exhibits tissue-specific isoforms with very close functional properties. We approached this problem by the purification of native betabeta-enolase from mouse hindlimb muscles and by raising specific antibodies of high titre against this protein. These reagents have been useful in revealing a heterogeneity of the beta-enolase subunit that changes with in vivo and in vitro maturation. A basic carboxypeptidase appears to be involved in generating an acidic beta-enolase variant, and may regulate plasminogen binding by this subunit. We show for the first time that pure betabeta-enolase binds with high affinity the adjacent enzymes in the glycolytic pathway (pyruvate kinase and phosphoglycerate mutase), favouring the hypothesis that these three enzymes form a functional glycolytic segment. betabeta-Enolase binds with high affinity sarcomeric troponin but not actin and tropomyosin. Some of these binding properties are shared by the alphaalpha-isoenolase, which is also expressed in striated muscle, but not by the neuron-specific gammagamma-enolase. These results support the idea that specific interactions with macromolecules will address muscle enolase isoforms at the subcellular site where ATP, produced through glycolysis, is most needed for contraction. Such a specific targeting could be modulated by post-translational modifications.

Alternative usage of exon 1 of bovine PrP mRNA

Here we report two types of bovine prion protein (PrP) mRNA that possessed different lengths of the 5'-untranslated region and were expressed in various bovine tissues. The two mRNA species were transcribed from identical positions but differed in the usage of the splice site for exon 1/intron. One mRNA possessed exon 1 consisting of 53 nucleotides and the other possessed exon 1 consisting of 168 nucleotides. Usage of exons 2 and 3 was identical for the two mRNA species. The two mRNA species were detected in all but spleen tissue; the mRNA possessing 168-nt exon 1 was not detected in bovine spleen. This is the first report on the tissue-specific alternative splicing of PrPc mRNA in any other species. Only a low level of PrPc appeared to be present in bovine spleen. These results suggested the possibility that the mRNA possessing 53-nt exon 1 was inefficiently translated into Prp; however, in vitro translation analysis showed no marked difference in translational efficiency between the two mRNA species.

Identification of pirin, a novel highly conserved nuclear protein

In this article we describe the molecular cloning of Pirin, a novel highly conserved 32-kDa protein consisting of 290 amino acids. Pirin was isolated by a yeast two-hybrid screen as an interactor of nuclear factor I/CCAAT box transcription factor (NFI/CTF1), which is known to stimulate adenovirus DNA replication and RNA polymerase II-driven transcription. Pirin mRNA is expressed weakly in all human tissues tested. About 15% of all Pirin cDNAs contain a short 34-base pair insertion in their 5'-untranslated regions, indicative of alternative splicing processes. Multiple Pirin transcripts are expressed in skeletal muscle and heart. Western blots and immunoprecipitations employing monoclonal anti-Pirin antibodies reveal that Pirin is a nuclear protein. Moreover, confocal immunofluorescence experiments demonstrate a predominant localization of Pirin within dot-like subnuclear structures. Homology searches using the BLAST algorithm indicate the existence of Pirin homologues in mouse and rat. The N-terminal half of Pirin is significantly conserved between mammals, plants, fungi, and even prokaryotic organisms. Genomic Southern and Western blots demonstrate the presence of Pirin genes and their expression, respectively, in all mammalian cell lines tested. The expression pattern, the concentrated localization in subnuclear structures, and its interaction with NFI/CTF1 in the two-hybrid system classify Pirin as a putative NFI/CTF1 cofactor, which might help to gain new insights in NFI/CTF1 functions.

The rat arylalkylamine N-acetyltransferase gene promoter. cAMP activation via a cAMP-responsive element-CCAAT complex

A 10-100-fold rhythm in the activity of arylalkylamine N-acetyltransferase (AA-NAT; EC 2.3.1.87) controls the rhythm in melatonin synthesis in the pineal gland. In some mammals, including the rat, the high nocturnal level of AA-NAT activity is preceded by an approximately 100-fold increase in AA-NAT mRNA. The increase in AA-NAT mRNA is generated by norepinephrine acting through a cAMP mechanism. Indirect evidence has suggested that cAMP enhances AA-NAT gene expression by stimulating phosphorylation of a DNA-binding protein (cAMP-responsive element (CRE)-binding protein) bound to a CRE. The nature of the sites involved in cAMP activation was investigated in this report by analyzing the AA-NAT promoter. An approximately 3700-base pair fragment of the 5'-flanking region of the rat AA-NAT gene was isolated, and the major transcription start points were mapped. The results of deletion analysis and site-directed mutagenesis indicate that cAMP activation requires a CRE.CCAAT complex consisting of a near-perfect CRE and an inverted CCAAT box located within two helical turns.