PRODUCTION OF SALMON-CALCITONIN-I IN ONCORHYNCHUS-GORBUSCHA BY ALTERNATIVE POLYADENYLATION OF 2 RNA SPECIES

RNAs of ultimobranchial bodies (U.B.) from the pink salmon, Oncorhynch us gorbuscha, were studied using the polymerase chain reaction (PCR) w ith specific oligodeoxyribonucleotides (oligos) of the salmon calciton in (sCT) mRNA selected in exon 2 or 3 and a poly(T) oligo. We observed two amplified DNA fragments, differing by 200 bp which hybridized wit h a specific exon 4 probe. Sequence analysis indicated that they both encoded exon 4, but differed in the length of their 3' non-coding regi ons by use of a putative polyadenylation signal situated 200 bp upstre am from the established polyadenylation site. These two polyadenylatio n signals very likely were regulated differently, as the larger expres sed transcript was predominant. To date, such use of an alternative po lyadenylation signal in a CT mRNA has not been described in other vert ebrates, and only the chicken CT mRNA possesses a second classical pol yadenylation signal which is not known to be used. This characteristic of sCT biosynthesis appears to be typical in lower vertebrates and is of phylogenic interest. Moreover, it engenders a hypothesis of a rela tionship between the high concentration of the peptide observed in fem ales of this species and their capacity to produce sCT by different bi osynthetic pathways.