PSEUDOGENES IN RIBONUCLEASE EVOLUTION - A SOURCE OF NEW BIOMACROMOLECULAR FUNCTION

Bovine seminal ribonuclease (RNase) diverged from pancreatic RNase aft er a gene duplication ca. 35 million years ago. Members of the seminal RNase gene family evidently remained as unexpressed pseudogene for mu ch of its evolutionary history. Between 5 and 10 million years ago, ho wever, after the divergence of kudu but before the divergence of ox, e vidence suggests that the pseudogene was repaired and expressed. Intri guingly, detailed analysis of the sequences suggests that the repair m ay have involved gene conversion, transfer of information from the pan creatic gene to the RNase pseudogene. Further, the ratio of non-silent to silent substitutions suggests that the pancreatic RNases are diver gently evolving under functional constraints, the seminal RNase pseudo genes are diverging under no functional constraints, while the genes e xpressed in the seminal plasma are evolving extremely rapidly in their amino acid sequences, as if to fulfil a new physiological role.