Isolation of the murine ribonuclease gene Rib-1: structure and tissue specific expression in pancreas and parotid gland.

The mouse pancreatic ribonuclease gene Rib-1 was isolated from a library of mouse genomic DNA and sequenced. This small gene contains a nontranslated exon of 52 base pairs, an intron of 791 base pairs, and a coding exon of 741 base pairs. Rib-1 transcripts were detected in parotid gland as well as in pancreas. The abundance of the transcripts were approximately 200-fold greater in pancreatic RNA than in parotid RNA. The sites of transcription initiation were mapped by primer extension and ribonuclease protection assays. One major initiation site and several minor initiation sites were identified in pancreatic RNA. Transcription in parotid appears to be initiated from the same sites. Parotid-specific transcripts were not detected. The data suggest that Rib-1 is transcribed in pancreas and parotid from the same promoter. This is in contrast with the mechanism for production of amylase in pancreas and parotid, which is accomplished by tissue specific expression of different gene copies.