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Pseudogenes in ribonuclease evolution: a source of new biomacromolecular function?

Bovine seminal ribonuclease (RNase) diverged from pancreatic RNase after a gene duplication ca. 35 million years ago. Members of the seminal RNase gene family evidently remained as unexpressed pseudogene for much of its evolutionary history. Between 5 and 10 million years ago, however, after the divergence of kudu but before the divergence of ox, evidence suggests that the pseudogene was repaired and expressed. Intriguingly, detailed analysis of the sequences suggests that the repair may have involved gene conversion, transfer of information from the pancreatic gene to the RNase pseudogene. Further, the ratio of non-silent to silent substitutions suggests that the pancreatic RNases are divergently evolving under functional constraints, the seminal RNase pseudogenes are diverging under no functional constraints, while the genes expressed in the seminal plasma are evolving extremely rapidly in their amino acid sequences, as if to fulfil a new physiological role.

Amino Acid Sequence↗

The size differences among mammalian introns are due to the accumulation of small deletions.

In order to investigate the molecular mechanisms that alter intron size, we conducted an extensive interspecies comparison of homologous introns among three mammalian groups: human, artiodactyls, and rodents. The size differences of introns were statistically significant among all three groups (longest intron was for human and shortest for rodents), and appear to be due to the accumulation of small deletions, according to the separate count of insertion and deletion frequencies. The distribution of intron size differences also has a shape similar to that for the distribution of insertion/deletion sizes found in pseudogenes. It is suggested that introns are selectively neutral to small-scale changes of the genome size, which inherently contain the bias of favoring short deletions against short insertions.

Animals↗