2 VARIANTS OF THE PITUITARY-SPECIFIC TRANSCRIPTION FACTOR PIT-1 IN ATLANTIC SALMON

We have cloned two 1.6 kb cDNAs encoding variants of the POU-type pitu itary-specific transcription factor Pit-1 from Atlantic salmon. Sequen ce comparison with mammalian Pit-1 revealed that the POU domain was hi ghly similar while flanking regions were less conserved. The N-termina l region contained three insertions relative to mammalian Pit-1, one o f these corresponded to the insertion found in the alternatively splic ed Pit-1a isoform. While two different salmon Pit-1 transcripts were e xpressed, alternative splicing in the 5'-region did not appear to cont ribute to further transcript diversity. Both salmon Pit-1 cDNAs encode d 39.5 kDa proteins that specifically bind a consensus Pit-1 recogniti on sequence in vitro. The salmon Pit-1 proteins also recognized the cl assical octamer motif; however, a point mutation in the POU homeodomai n abolished this interaction.