MOLECULAR EVOLUTION OF GENES ENCODING RIBONUCLEASES IN RUMINANT SPECIES

Phylogenetic analysis, based on the primary structures of mammalian pa ncreatic-type ribonucleases, indicated that gene duplication events, w hich occurred during the evolution of ancestral ruminants, gave rise t o the three paralogous enzymes present in the bovine species. Herein w e report data that demonstrate the existence of the orthologues of the bovine pancreatic, seminal, and cerebral ribonucleases coding sequenc es in the genomes of giraffe and sheep. The ''seminal'' sequence is a pseudogene in both species. We also report an analysis of the transcri ptional expression of ribonuclease genes in sheep tissues. The data pr esented support a model for positive selection acting on the molecular evolution of ruminant ribonuclease genes.