The fission yeast rpa17(+) gene encodes a functional homolog of AC19, a subunit of RNA polymerases I and III of Saccharomyces cerevisiae

Eukaryotic RNA polymerases I and III consist of multiple subunits. Each of these enzymes includes two distinct and evolutionarily conserved subunits c alled alpha-related subunits which are shared only by polymerases I and III . The alpha-related subunits show limited homology with the alpha-subunit: of prokaryotic RNA polymerase. To gain further insight into the structure a nd function of alpha-related subunits, we cloned and characterized a gene f rom Schizosaccharomyces pombe that encodes a protein of 17 kDa which call f unctionally replace AC19 - an alpha-related subunit of RNA polymerases I an d III of Saccharomyces cerevisiae - and was thus named rpa17(+). RPA17 has 125 amino acids and shows 63% identity to AC19 over a 108-residue stretch, whereas the N-terminal regions of the two proteins are highly divergent. Di sruption of rpa17(+) shows that the gene is essential for cell growth. Sequ ence comparison with other alpha-related subunits from different species sh owed that RPA17 contains an 81-amino acid block that is evolutionarily cons erved. Deletion analysis of the N- and C-terminal regions of RPA 17 and AC1 9 confirms that the 81-amino acid block is important for the function of th e alpha-related subunits.