Age and detection of retroprocessed pseudogenes in murine rodents

Retroprocessed pseudogenes, calmodulin II (psi (1), psi (2), and psi (3) CA LMII), psi alpha -tubulin, pi -glutathione S-transferase (psi pi -GST) from rat, lactic acid dehydrogenase (psi LDH) from mouse, and heat shock protei n 60 chaperonin (psi HSP60) from Chinese hamster, were examined for their p resence in these species by polymerase chain reaction (PCR). Pseudogenes of these murine rodents were detected by PCR only in those species in which t he genes were originally identified, suggesting that the selected pseudogen e of one species arose too recently to be detected in the genomes of the ot her rodent species. The calculated ages of the rodent pseudogenes ranged fr om 1.7 Myr (psi alpha -tubulin) to 7.5 Myr (psi (3) CALMII) when employing a homologous functional gene of the taxon as a reference in the relative ra te test with the mouse or rat as the outgroup. Given the high rate of diver gence of the genes of rodents relative to other species, selection of an ou tgroup with similar mutation rates seems warranted. To justify further the conclusion that the selected pseudogenes were indeed retroprocessed after t hese three taxa diverged, the presence of the pseudogenes in the genome of different rat species was examined. The existence of psi (3) CALMII and psi alpha -tubulin pseudogenes of Rattus norvegicus among species belonging to Rattus sensu stricto is evidence for the common ancestry of this group.