Isolation, Characterization, and Evolutionary Divergence of Mouse RNase 6: Evidence for Unusual Evolution in Rodents

Abstract

The evolution of the ribonuclease A (RNase A) vertebrate-specific enzyme family is interesting in that specific gene lineages appear to be responding to unique selective pressures in wildly diverse manners to generate proteins that are capable of reducing the infectivity of viruses, killing systemic pathogens, and inducing the growth of blood vessels all while maintaining the signature motifs of a ribonuclease. In this paper, we present the DNA sequence and gene structure of Mus musculus RNase 6 and examine the expression pattern and enzymatic activity of the recombinant protein. M. musculus RNase 6 has a limited expression pattern compared to human RNase 6 and is an efficient ribonuclease, with a catalytic efficiency 17-fold higher than that of human protein. Evo- lutionary analysis reveals that RNase 6 was subject to unusual evolutionary forces ( d N / d S = 1.2) in an ancestral rodent lineage before the separation of Mus and Rattus . However, more recent evolution of rodent RNase 6 has been relatively conserved, with an average d N / d S of 0.66. These data suggest that the ancestral rodent RNase 6 was subject to accelerated evolution, resulting in the conserved modern gene, which most likely plays an important role in mouse physiology.