Novel structure of a Chinese hamster polyubiquitin gene

We isolated a polyubiquitin gene, CHUB2, from the V79 Chinese hamster genomic library, and determined its complete structure. Based on sequence homology to the human polyubiquitin gene UbC in the 5' and 3' untranslated region, the CHUB2 gene was characterized as the V79 Chinese hamster equivalent to the human UbC gene. However, the overall coding region structure of the CHUB2 gene was altered from the consensus structure of polyubiquitin genes, with the last ubiquitin coding unit being followed by 161 bp of partially deleted and mutated ubiquitin-like sequence. Although a similarly deleted and mutated polyubiquitin gene was recently reported in a partially sequenced cDNA of mouse (Finch et al. (1992) Cell Growth Differ. 3, 269-278), the present study describes the complete sequence of a polyubiquitin gene containing this unusual structure for the first time, and suggests that this structure is conserved in rodents. By employing both Southern and Northern analysis with a probe specific to the CHUB2 gene, it was found that a second, closely related gene is present in the Chinese hamster genome, and that both loci are transcriptionally active in V79 cells. The two genes, and their respective transcripts, differ in size because of variation in the relative number of repeating ubiquitin coding units.