Isolation and characterization of the fission yeast gene rpa42 super(+), which encodes a subunit shared by RNA polymerases I and III

• Published in: Molecular & general genetics Vol. 262; no. 4/5; pp. 749 - 757
• Main Authors: Imazawa, Y, Imai, K, Fukushima, A, Hisatake, K, Muramatsu, M, Nogi, Y
• Format: Journal Article
• Language: English
• Published: 15.12.1999
• Subjects: Escherichia coli; rpa42 gene; RPA42 protein; Saccharomyces cerevisiae; Schizosaccharomyces pombe
• ISSN: 0026-8925

Eukaryotic RNA polymerases I and III share two distinct alpha -related subunits that show limited homology to the alpha subunit of Escherichia coli RNA polymerase, which forms a homodimer to nucleate the assembly of prokaryotic RNA polymerase. To gain insight into the functions of alpha -related subunits in eukaryotes, we have previously identified the alpha -related small subunit RPA17 of RNA polymerase I (and III) in Schizosaccharomyces pombe, and have shown that it is a functional homolog of Saccharomyces cerevisiae AC19. In an extension of that study, we have now isolated and characterized rpa42 super(+), which encodes the alpha -related large subunit RPA42 of S. pombe RNA polymerase I, by virtue of the fact that its product interacts with RPA17 in the yeast two-hybrid system. We have found that rpa42 super(+) encodes a polypeptide with an apparent molecular mass of 42 kDa, which shows 58% identity to the AC40 subunit shared by RNA polymerases I and III in S. cerevisiae. Furthermore, we have shown that rpa42 super(+) complements a temperature-sensitive mutation in RPC40 the gene that encodes AC40 in S. cerevisiae and which is essential for cell growth. Finally, we have shown that neither RPA42 nor RPA17 can self-associate. These results provide evidence that the two distinct alpha -related subunits, RPA42 and RPA17, of RNA polymerases I and III are functionally conserved between S. pombe and S. cerevisiae, and suggest that heterodimer formation between them is essential for the assembly of RNA polymerases I and III in eukaryotes.