The bovine protamine 2 gene: evidence for alternative splicing.

Protamine 2 (PRM2) is a low molecular weight arginine-rich protein which is present in haploid spermatogenic cells of human and mouse. Although the bull PRM2 gene is translated and transcribed at low levels, the protein could not be detected. The gene was isolated from a cosmid library and was found to consist of two exons (298 and 50 bp, respectively) interrupted by an intron of 142 bp. As compared to the PRM2 genes of man, mouse and rat the bovine gene lacks a highly conserved sequence coding for the amino acids RLHRIH. Furthermore, primer extension experiments on bull PRM2 mRNA and sequencing of junction fragments revealed alternative splicing of mRNA resulting in two putative isoforms of the protein. The most abundant transcript is spliced at the conserved splice donor site found in exon 1 at position 236 giving rise to an in-frame deletion of 63 bp as compared to the cDNA sequence (Maier et al. (1990) Nucleic Acids Res. 18, 1249-1254). The less abundant longer mRNA was not detectable by radioactive primer extension. The corresponding cDNA was obtained by performing PCR with reverse transcribed bull testis RNA or with a spermatid specific cDNA library. Alternative splicing should result in an addition of 21 nonpolar amino acids in the derived polypeptide and an altered protein conformation and function.