부산대학교 도서관

ABSTRACTBoth the gene and the cDNA encoding the Rpb4 subunit of RNA polymerase II were cloned from the fission yeastSchizosaccharomyces pombe. The cDNA sequence indicates that Rpb4 consists of 135 amino acid residues with a molecular weight of 15,362. As in the case of the corresponding subunits from higher eukaryotes such as humans and the plant Arabidopsis thaliana, Rpb4 is smaller than RPB4 from the budding yeastSaccharomyces cerevisiaeand lacks several segments, which are present in the S. cerevisiaeRPB4 subunit, including the highly charged sequence in the central portion. The RPB4 subunit ofS. cerevisiaeis not essential for normal cell growth but is required for cell viability under stress conditions. In contrast,S. pombeRpb4 was found to be essential even under normal growth conditions. The fraction of RNA polymerase II containing RPB4 in exponentially growing cells of S. cerevisiaeis about 20%, but S. pombeRNA polymerase II contains the stoichiometric amount of Rpb4 even at the exponential growth phase. In contrast to the RPB4 homologues from higher eukaryotes, however, S. pombeRpb4 formed stable hybrid heterodimers with S. cerevisiaeRPB7, suggesting that S. pombeRpb4 is similar, in its structure and essential role in cell viability, to the corresponding subunits from higher eukaryotes. However, S. pombeRpb4 is closer in certain molecular functions to S. cerevisiaeRPB4 than the eukaryotic RPB4 homologues.