SYNTHESIS OF TURKEY PIT-1 MESSENGER-RNA VARIANTS BY ALTERNATIVE SPLICING AND TRANSCRIPTION INITIATION

The gene encoding turkey Pit-1/GHF-1 (tPit-1) spans approximately 12 k ilobases (kb) and consists of 7 exons. One exon, which is located betw een exons 2 and 3, is designated exon 2a and codes for 38 amino acids not found in mammalian Pit-1. Because all tPit-1 variants contain exon 2a, they are denoted with an asterisk () to distinguish them from co mparable mammalian Pit-1s. Three tPit-1 variants are generated by alte rnative splicing and transcription initiation. Splicing of exon 1 to a n alternative acceptor splice site in exon 2 results in a 28 amino aci d insertion in tPit-1 beta relative to tPit-1*. A transcript unique t o the turkey has been identified by RT-PCR and RNase mapping. This tra nscript, designated tPit-1W, arises following transcription initiatio n upstream of the alternative acceptor splice site in exon 2. In turke y pituitary, the mRNA for the tPit-1 variant is the most abundant, th e tPit-1W variant is intermediate, and the tPit-1 beta* variant is th e least abundant.