Functional characterization of ABC10alpha, an essential polypeptide shared by all three forms of eukaryotic DNA-dependent RNA polymerases.
ABC10alpha is a small polypeptide shared by the three yeast RNA polymerases. Homologous polypeptides in higher eukaryotes have a zinc-binding CX(2)C. CX(2)C motif and a conserved basic C-terminal end. These features are also found in archaeal gene products that may encode an RNA polymerase subunit. The CX(2)C. CX(2)C motif is partly dispensable, since only its first cysteine is essential for growth, whereas the basic C-terminal end is critical in vivo. A mutant in the latter domain has an RNA polymerase III-specific defect and, in vitro, impairs RNA polymerase III assembly. Polymerase activity was, however, not affected in various faithful transcription assays. The mutant is suppressed by a high gene dosage of the second largest subunit of RNA polymerase III, whereas the homologous subunits of RNA polymerase I and II have aggravating effects. In a two-hybrid assay, ABC10alpha binds to the C-terminal half of the second largest subunit of RNA polymerase I, in a way that requires the integrity of the CX(2)C. CX(2)C motif. Thus, ABC10alpha appears to interact directly with the second largest subunit during polymerase assembly. This interaction is presumably a major rate-limiting step in assembly, since diploid cells containing only one functional gene copy for ABC10alpha have a partial growth defect.
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Service de Biochimie et Génétique Moléculaire, Bât. 142, Commissariat à l'Energie Atomique, CEA/Saclay, Gif sur Yvette, F-91191 Cedex, France.
Labarre-Mariotte
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Chédin
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Thuriaux
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D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000201:enzymology; D002455:Cell Division; D017124:Conserved Sequence; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000201:enzymology*; D018628:Gene Dosage; D006801:Humans; D016296:Mutagenesis; D011485:Protein Binding; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D012320:RNA Polymerase III / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D012568:Schizosaccharomyces / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D014158:Transcription, Genetic
D012319:RNA Polymerase II; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I; D012320:RNA Polymerase III