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 have recently generated novel rat transgenic lines carrying an arylalkylamine N-acetyltransferase (AA-NAT) promoter-reporter construct in which CAT (with 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 utilises 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 analysis has shown that protein deriving from an aberrant open reading frame is not expressed at detectable levels.