PRODUCTION OF SVP-1 -3/-4 IN GUINEA-PIG TESTIS - CHARACTERIZATION OF NOVEL TRANSCRIPTS CONTAINING LONG 5'-UNTRANSLATED REGIONS AND MULTIPLEUPSTREAM AUG CODONS/

The GP1G gene of the guinea pig codes for three of the four abundant s eminal vesicle secretory proteins produced in this species, This gene is expressed at highest efficiency in the seminal vesicle (SV) from a promoter that contains a canonical TATA box and CCAAT box. However, GP 1G gene transcripts and proteins have also been identified in other ti ssues. To investigate the structure of GP1G transcripts produced in th e testis, cDNA clones were isolated by screening a testis library. Thr ee unique cDNAs (TSM1-3) were isolated. Each of these clones contained a 3'-untranslated region (UTR) and coding region identical to that of the seminal vesicle transcript. However, the 5'-UTRs of the testis tr anscripts were significantly longer than that found on the SV mRNA (41 6-646 nucleotides compared with only 23 nucleotides for the SV). Each of these alternatively spliced 5'-UTRs incorporated the SV promoter el ements into transcribed sequence, and each contained multiple upstream AUG codons predicted to abolish translation of the major open reading frame. Nevertheless, each of the testis transcripts was capable of di recting the synthesis of GP1G-related proteins in vitro. Analysis of t he translation products suggests that the extended 8'-UTR of the testi s transcripts regulate both the choice of translation start site and t he efficiency of translation in this system. Western blot analysis of testis proteins revealed that the protein products of GP1G are also sy nthesized by the testis in vivo.