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 seque nce homology to the human polyubiquitin gene UbC in the 5' and 3' untr anslated region, the CHUB2 gene was characterized as the V79 Chinese h amster equivalent to the human UbC gene. However, the overall coding r egion structure of the CHUB2 gene was altered from the consensus struc ture of polyubiquitin genes, with the last ubiquitin coding unit being followed by 161 bp of partially deleted and mutated ubiquitin-like se quence. Although a similarly deleted and mutated polyubiquitin gene wa s recently reported in a partially sequenced cDNA of mouse (Finch et a l. (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 con served in rodents. By employing both Southern and Northern analysis wi th a probe specific to the CHUB2 gene, it was found that a second, clo sely related gene is present in the Chinese hamster genome, and that b oth 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.