VARIOUS TRANSCRIPTS ARE GENERATED FROM THE VCSA1 GENE BY ALTERNATIVE SPLICING AND POLY(A) PROCESSING IN THE RAT SUBMANDIBULAR-GLAND

The members of the VCS (variable coding sequence) multigene family dis play extensive evolutionary divergence in the protein-coding region. T he first described gene (VCSA1) was found to encode a major 0.7-kb mRN A (VCSA11T1) coding for a prohormone-like preproprotein, SMR1-VA1, in the submandibular gland (SMG) of Rattus norvegicus. We report here th e cloning of four other VCSA1 cDNAs corresponding to mRNAs (VCSA11T2 to 1T5) expressed in the SMG, VCSA1*1T1 to *1T4 mRNAs share the three exons previously described and differ in their 3' untranslated region s (UTR). Their differences originate from the alternative utilization of four polyadenylation sites. Comparison of the tissue levels of VCSA 11T1 and VCSA1*1T4 during post-natal development of the male rat SMG suggests that the poly(A) addition sites are both used at each stage. The fifth RNA transcript (VCSA11T5) contains only the first two exons . The nucleotide sequence of the cDNA reveals that VCSA1 has an additi onal exon (exon 4) which is spliced to exon 2 in VCSA11T5. In additio n to VCSA11T1, at least VCSA1*1T4 and VCSA1*1T5 are actively translat ed in vivo, as revealed by their association to the polysomal fraction s. The protein, P2-VA1, coded by VCSA11T5 is 68 amino acids in length and it is likely to be a glycosylated secretory protein. The putative mature P2-VA1 protein completely differs from the SMR1-VA1 pro-protei n and very likely has a different function. VCSA11T1 is accumulated i n the male rat SMG 200-1000-fold more than the other transcripts, Run- on experiments reveal that almost all transcription proceeds several h undred bp downstream from the poly(A) site corresponding to VCSA11T1. This suggests that the high levels of VCSA11T1 transcript are mainly due to post-transcriptional events.