Secretory ribonucleases in the primitive ruminant chevrotain (Tragulus javanicus)

Phylogenetic analyses of secretory ribonucleases or RNases 1 have shown tha t gene duplication events, giving rise to three paralogous genes (pancreati c, seminal and brain RNase), occurred during the evolution of ancestral rum inants. A higher number of paralogous sequences are present in chevrotain ( Tragulus javanicus), the earliest diverged taxon within the ruminants. Two pancreatic RNase sequences were identified, one encoding the pancreatic enz yme, the other encoding a pseudogene. The identity of the pancreatic enzyme was confirmed by isolation of the protein and N-terminal sequence analysis . It is the most acidic pancreatic ribonuclease identified so far. Formatio n of the mature enzyme requires cleavage by signal peptidase of a peptide b ond between two glutamic acid residues. The seminal-type RNase gene shows f eatures of a pseudogene, like orthologous genes in other ruminants investig ated with the exception of the bovine species. The brain-type RNase gene of chevrotain is expressed in brain tissue. A hybrid gene with a pancreatic-t ype N-terminal and a brain-type C-terminal sequence has been identified but nothing is known about its expression. Phylogenetic analysis of RNase I se quences of six ruminant, three other artiodactyl and two whale species supp ort previous findings that two gene duplications occurred in a ruminant anc estor. Three distinct groups of pancreatic, seminal-type and brain-type RNa ses have been identified and within each group the chevrotain sequence it t he first to diverge. In taxa with duplications of the RNase gene (ruminants and camels) the gene evolved at twice as fast than in taxa in which only o ne gene could be demonstrated; in ruminants there was an approximate to fou rfold increase directly after the duplications and then a slowing in evolut ionary rate.