THE EVOLUTION OF PROTAMINE P1 GENES IN DASYURID MARSUPIALS

We report the complete DNA sequences of the protamine P1 gene and flan king regions for 13 species of the marsupial family Dasyuridae. The st ructure of the protamine locus is conserved in dasyurids and consists of two exons (of lengths 142-151 and 47 bp) separated by an intron (20 8-240 bp), A key feature of the dasyurid intron is a 38-40 bp duplicat ion found in all species examined to date, This duplication apparently predates the radiation of modern dasyurid lineages and may be homolog ous to a similar feature in the marsupial mole (Notoryctes). Sequences from a species of Planigale demonstrate that this genus is unique amo ng marsupials in possessing cysteine residues in its protamine Pl mole cules. Cysteines may provide enhanced chemical stability for condensed sperm nuclei, a physiological feature that would converge on the comm on eutherian pattern. Phylogenetic analysis of the protamine genes yie lds a tree that is largely congruent with previous molecular systemati c studies in two areas: (1) There are three main dasyurid lineages cor responding to the Sminthopsinae, Dasyurinae, and Phascogalinae; (2) Da syurinae and Phascogalinae are sister groups, This study is the first estimate of dasyurid relationships based on a nuclear DNA sequence.