The fission yeast RPA21 subunit of RNA polymerase I: an evolutionarily conserved subunit interacting with ribosomal DNA (rDNA) transcription factor Rrn3p for recruitment to rDNA promoter.
Recruitment of RNA polymerases to the cognate promoter is a key step for the transcription initiation of specific genes in eukaryotes. Recently, RNA polymerase I (pol I) of Saccharomyces cerevisiae was shown to be recruited to the rDNA promoter via interaction between Rrn3p, a conserved transcription factor for rDNA, and A43, a subunit specific to pol I. The question of whether a similar interaction for pol I recruitment is conserved in other eukaryotes remains to be answered. We show here that Schizosaccharomyces pombe rpa21(+) encodes a protein of apparent molecular mass 21 kD which shows 36% identity to the A43 subunit of pol I in S. cerevisiae, and that rpa21(+) is essential for cell growth. To gain further insight into the functions of RPA21, we isolated a total of 22 temperature-sensitive (ts) mutants of rpa21(+) and found that most of the substitutions causing the ts phenotype are clustered in the N-terminal half of RPA21. The ts mutants showed a markedly reduced amount of primary transcripts of rDNA immediately after temperature shift-up. Over-expression of S. pombe rrn3(+) in the ts mutants suppressed the growth defect in an allele-specific manner. Therefore, we conclude that S. pombe RPA21 plays a functional role similar to that of A43 in S. cerevisiae and that the mechanism of recruitment of pol I to the rDNA promoter by the interaction of a specific pol I subunit with Rrn3p is evolutionarily conserved.
Imazawa
Yukiko
Y
CREST, Japan Science and Technology Corporation Center, Kawaguchi, Saitama, 332-0012, Japan.
Hisatake
Koji
K
Nakagawa
Kaori
K
Muramatsu
Masami
M
Nogi
Yasuhisa
Y
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004275:DNA, Ribosomal; D006358:Hot Temperature; D008969:Molecular Sequence Data; D009154:Mutation; D035463:Pol1 Transcription Initiation Complex Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012318:RNA Polymerase I / Q000235:genetics* / Q000378:metabolism; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
D004275:DNA, Ribosomal; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I