The fission yeast protein Ker1p is an ortholog of RNA polymerase I subunit A14 in Saccharomyces cerevisiae and is required for stable association of Rrn3p and RPA21 in RNA polymerase I.
A heterodimer formed by the A14 and A43 subunits of RNA polymerase (pol) I in Saccharomyces cerevisiae is proposed to correspond to the Rpb4/Rpb7 and C17/C25 heterodimers in pol II and pol III, respectively, and to play a role(s) in the recruitment of pol I to the promoter. However, the question of whether the A14/A43 heterodimer is conserved in eukaryotes other than S. cerevisiae remains unanswered, although both Rpb4/Rpb7 and C17/C25 are conserved from yeast to human. To address this question, we have isolated a Schizosaccharomyces pombe gene named ker1+ using a yeast two-hybrid system, including rpa21+, which encodes an ortholog of A43, as bait. Although no homolog of A14 has previously been found in the S. pombe genome, functional characterization of Ker1p and alignment of Ker1p and A14 showed that Ker1p is an ortholog of A14. Disruption of ker1+ resulted in temperature-sensitive growth, and the temperature-sensitive deficit of ker1delta was suppressed by overexpression of either rpa21+ or rrn3+, which encodes the rDNA transcription factor Rrn3p, suggesting that Ker1p is involved in stabilizing the association of RPA21 and Rrn3p in pol I. We also found that Ker1p dissociated from pol I in post-log-phase cells, suggesting that Ker1p is involved in growth-dependent regulation of rDNA transcription.
Imazawa Y, Hisatake K, Mitsuzawa H, Matsumoto M, Tsukui T, Nakagawa K, Nakadai T, Shimada M, Ishihama A, Nogi Y