Isolation and characterization of the fission yeast gene Sprpa12(+) reveals that the conserved C-terminal zinc-finger region is dispensable for the function of its product

RNA polymerase I of Saccharomyces cerevisiae contains a small subunit, A12. 2, encoded by RPA12, that was previously shown to be involved in the assemb ly and/or stabilization of the largest subunit, A190, of RNA polymerase I. To examine whether an equivalent subunit is present in another eukaryotic R NA polymerase I, we have cloned a Schizosaccahromyces pombe cDNA that is ab le to complement the rpa12 mutation in S. cerevisiae. The gene, named Sprpa 12(+), encodes a polypeptide of 119 amino acids that shows 55% identity to S. cerevisiae A12. 2 over its entire length, including two zinc-finger moti fs. Disruption of the chromosomal Sprpa12(+) gene shows that it is required for growth at higher temperatures but not at lower temperatures. Expressio n of Sprpa190(+)/nuc1(+), which encodes the largest subunit of the S. pombe RNA polymerase I, from a multicopy plasmid can partially suppress the grow th defect of the Sprpa12 disruptant at higher temperatures. These findings suggest that A12.2 subunit is functionally and structurally conserved betwe en S. cerevisiae and S. pombe. Finally, the analysis of mutants suggests th at SpRPA12 requires the zinc-finger domain in the N-terminal region but not the one in the C-terminal region for its function.