A heterodimer formed by the A14 and A43 subunits (A14/A43) of RNA polymerase I1 (pol I) in Saccharomyces cerevisiae is proposed to correspond to the Rpb4/Rpb7 and C17/C25 heterodimers in RNA polymerases II and 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 yeasts 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 an alignment between Ker1p and A14 show that Ker1p is an ortholog of A14. Disruption of ker1+ results in temperature-sensitive (ts) growth and the ts-deficit of ker1D is suppressed by either overexpression of 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 dissociates from pol I in post-log-phase cells, suggesting that Ker1p is involved in growth-dependent regulation of rDNA transcription.