Functional isoforms of Pit-1 generated by alternative messenger RNA splicing.

Pit-1 is a pituitary-specific transcription factor that activates expression of the GH and PRL genes. We have isolated a cDNA encoding a variant isoform of Pit-1 that we term Pit-1 beta. Pit-1 beta contains an insertion of 26 amino acids in the transactivation domain as a consequence of the utilization of an alternative 3' splice acceptor at the end of the first intron. Like the previously described Pit-1 alpha, Pit-1 beta transactivates both the GH and PRL promoters. However, the larger isoform acts as a more potent inducer of GH.