Seminal-type ribonuclease genes in ruminants, sequence conservation without protein expression?

Bovine seminal ribonuclease (BS-RNase) is an interesting enzyme both for fu nctional and structural reasons. The enzyme is the product of a gene duplic ation that occurred in an ancestral ruminant. It is possible to demonstrate the presence of seminal-type genes in all other investigated ruminant spec ies, but they are not expressed and show features of pseudogenes. In this p aper we report the determination of two pancreatic and one seminal-type rib onuclease gene sequences of swamp-type water buffalo (Bubalus bubalis). The two pancreatic sequences encode proteins with identical amino acid sequenc es as previously determined for the enzymes isolated from swamp-type and ri ver-type water buffalo, respectively. The seminal-type sequence has no pseudogene features and codes for an enzym e with no unusual features compared with the active bovine enzyme, except f or the replacement of one of the cysteines which takes part in the two inte rsubunit disulfide bridges. However, Western blotting demonstrates the pres ence of only small amounts of the pancreatic enzymes in water buffalo semen , suggesting that also in this species the seminal-type sequence is not exp ressed. But it is still possible that the gene is expressed somewhere else in the body or during development. Reconstruction of seminal-type ribonuclease sequences in ancestors of Bovin ae and Bovidae indicates no serious abnormalities in the encoded proteins a nd leads us to the hypothesis that the ruminant seminal-type ribonuclease g ene has not come to expression during most of its evolutionary history, but did not exhibit a high evolutionary rate that is generally observed in pse udogenes. (C) 1999 Elsevier Science B.V. All rights reserved.