Characterization of the testes-specific pim-1 transcript in rat

The pim-1 proto-oncogene encodes a serine/threonine protein kinase and is expressed in cells of hematolymphoid origin and in the germ cell lineages. In somatic cells, the pim-1 gene is expressed as a 2.8 kb transcript while a shorter sized transcript (2.3 kb) is expressed in rat testes. We have determined that the shorter testes-specific pim-1 transcript arises through the use of an alternate polyadenylation signal present in the 3' untranslated region of the gene. This alternate polyadenylation event results in the removal of an A/U-rich regulatory element located in the 3' untranslated region of the pim-1 gene. This A/U-rich motif has been shown by a number of laboratories to destabilize the transcripts of genes that contain this sequence. Consistent with these findings, we have demonstrated that the shortened testes-specific pim-1 transcript is more stable than the longer A/U-rich containing somatic transcript. We suggest that the functional significance of different sized pim-1 transcripts may be directly related to their different stabilities and that the greater stability of the testes-specific transcript may be essential for the translational delay observed in post-meiotic male germ cells.