Differential distribution of the P1 and P2 protamine gene sequences in eutherian and marsupial mammals and a monotreme

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Abstract
At the protein level, the P1 protamine is the predominant form of mammalian protamine, present in all mammalian spermatozoa analyzed to date. An additional variant, the P2 protamine, has been detected only in spermatozoa of the mouse, hamster and human. Southern blot analysis of a group of restriction enzyme‐digested mammalian DNAs has revealed the presence of sequences homologous to the P1 and the P2 mouse protamine genes in diverse species. In agreement with protein studies, nucleotide sequences homologous to the mouse P1 protamine cDNA are widespread, being present in the genomic DNAs of human, rat, dog, ram, horse, bull, hamster, baboon, flying fox (megabat), microbat, boar, North American opossum, and wallaby. Although we detect genomic sequences with strong homology to the mouse protamine 2 cDNA in rat and hamster, we also find weaker but reproducible hybridization to the genomic DNA of human, boar, dog, bull, microbat, wallaby, and platypus. With the exception of the human, the P2 protamine has not been detected in the spermatozoa of these latter species.