Use of a cryptic splice donor site in the chloramphenicol acetyltransferase (CAT)-SV40 small-t antigen cassette generates alternative transcripts in transgenic rats

The bacterial gene chloramphenicol acetyltransferase (CAT) is a widely used reporter in both in-vitro and in-vivo studies of genetic regulation. We ha ve recently generated novel rat transgenic lines carrying an arylalkylamine N-acetyltransferase (AA-NAT) promoter-reporter construct in which CAT (wit h associated SV40 small-t antigen sequence) is the reporter. In addition to the predicted transgene transcript (1.9 kb), we identified an abundant 1.5 kb transcript which derives from an alternative splicing event that utilis es a cryptic splice donor site located within the CAT gene. The native CAT open reading frame (ORF) is lost in the 1.5 kb transcript, and a western an alysis has shown that protein deriving from an aberrant open reading frame is not expressed at detectable levels.