Divergence of protamine gene sequences in fish.

Complementary DNA to trout protamine mRNA was hybridized to excess genomic DNA from trout, salmon and yellow perch. Although there was extensive hybridization of the cDNA to trout DNA, no cross-reaction with yellow perch DNA was observed and the hybridization to salmon DNA was noticeably less than in the homologous reaction. To confirm these results, yellow perch protamine mRNA was purified and compared directly to trout protamine mRNA. Yellow perch protamine mRNA was shorter than trout protamine mRNA, when measured by agarose gel electrophoresis in the presence of methyl mercury hydroxide. The two mRNAs did not cross-react in cDNA/RNA hybridizations, although the homologous reactions went to 90% of completion. This lack of sequence homology was confirmed when the oligopyrimidine tracts from the cDNAs were compared. No sequences longer than tetranucleotides were common to both species. Trout protamine cDNA contained oligopyrimidines of composition C7T4, C4T2, C3T2, C2T3, C1T5 and C1T4 whereas yellow perch protamine cDNA contained C6T3 and C4T3.