Inclusion of Cetaceans within the order Artiodactyla based on phylogenetic analysis of pancreatic ribonuclease genes

Mammalian secretory ribonucleases (RNases 1) form a family of extensively studied homologous proteins that were already used for phylogenetic analyses at the protein sequence level previously. In this paper we report the determination of six ribonuclease gene sequences of Artiodactyla and two of Cetacea. These sequences have been used with ruminant homologues in phylogenetic analyses that supported a group including hippopotamus and toothed whales, a group of ruminant pancreatic and brain-type ribonucleases, and a group of tylopod sequences containing the Arabian camel pancreatic ribonuclease gene and Arabian and Bactrian camel and alpaca RNase 1 genes of unknown function. In all analyses the pig was the first diverging artiodactyl. This DNA-based tree is compatible to published trees derived from a number of other genes, The differences to those trees obtained with ribonuclease protein sequences can be explained by the influence of convergence of pancreatic RNases from hippopotamus, camel, and ruminants and by taking into account the information from third codon positions in the DNA-based analyses, The evolution of sequence features of ribonucleases such as the distribution of positively charged amino acids and of potential glycosylation sites is described with regard to increased double-stranded RNA cleavage that is observed in several cetacean and artiodactyl RNases which may have no role in ruminant or ruminant-like digestion

EVOLUTION AND RECOMBINATION OF BOVINE DNA REPEATS

The history of the abundant repeat elements in the bovine genome has been studied by comparative hybridization and PCR. The Bov-A and Bov-B SINE elements both emerged just after the divergence of the Camelidae and the true ruminants. A 31-bp subrepeat motif in satellites of the Bovidae species cattle, sheep, and goat is also present in Cervidae (deer) and apparently predates the Bovidae. However, the other components of the bovine satellites were amplified after the divergence of the cattle and the Caprinae (sheep and goat). A 23-bp motif, which as subrepeat of two major satellites occupies 5% of the cattle genome, emerged only after the split of the water buffalo and other cattle species. During the evolution of the Bovidae the satellite repeat units were shaped by recombination events involving subrepeats, other satellite components, and SINE elements. Differences in restriction sites of homologous satellites indicate a continuing rapid horizontal spread of new sequence variants