Higher frequency of concerted evolutionary events in rodents than in man at the polyubiquitin gene VNTR locus

The polyubiquitin gene is an evolutionarily conserved eukaryotic gene, encoding tandemly repeated multiple ubiquitins, and is considered to be subject to concerted evolution. Here, we present the nucleotide sequences of new alleles of the polyubiquitin gene UbC in humans and CHUB2 in Chinese hamster, which encode a different number of ubiquitin units from those of previously reported genes. And we analyze the concerted evolution of these genes on the basis of their orthologous relationship. That the mean of the synonymous sequence difference [K.sub.s], which is defined as the number of synonymous substitution relative to the total number of synonymous sites, within the UbC and CHUB2 genes (0.192 [+ or -] 0.096) is significantly less than [K.sub.s] between these genes (0.602 [+ or -] 0.057) provides direct evidence for concerted evolution. Moreover, it also appears that concerted evolutionary events have been much more frequent in CHUB2 than in UbC, because [K.sub.s] within CHUB2 (0.022 [+ or -] 0.018) is much less than that within UbC (0.362 [+ or -] 0.192). By a numerical simulation, postulating that the major mechanism of concerted evolution in polyubiquitin genes is unequal crossing over, we estimated the frequency of concerted evolutionary events of CHUB2 at 3.3 X [10.sup.-5] per year and that of UbC at no more than 5.0 x [10.sup.-7] per year.