4 SUBUNITS THAT ARE SHARED BY THE 3 CLASSES OF RNA-POLYMERASE ARE FUNCTIONALLY INTERCHANGEABLE BETWEEN HOMO-SAPIENS AND SACCHAROMYCES-CEREVISIAE

Four cDNAs encoding human polypeptides hRPB7.0, hRPB7.6, hRPB17, acid hRPB14.4 (referred to as Hs10 alpha, Hs10 beta, Hs8, and Hs6, respecti vely), homologous to the ABC10 alpha, ABC10 beta, ABC14.5, and ABC23 R NA polymerase subunits (referred to as Sc10 alpha, Sc10 beta, Sc8, and Sc6, respectively) of Saccharomyces cerevisiae, were cloned and chara cterized for their ability to complement defective yeast mutants. Hs10 alpha and the corresponding Sp10 alpha of Schizosaccharomyces pombe c an complement an S. cerevisiae mutant (rpc10-Delta::HIS3) defective in Sc10 alpha. The peptide sequences are highly conserved in their carbo xy-terminal halves, with an invariant motif CX(2)CX(12)RCX(2)CGXR corr esponding to a canonical zinc-binding domain. Hs10 beta, Sc10 beta, an d the N subunit of archaeal RNA polymerase are homologous. An invarian t CX(2)CGX(n)CCR motif presumably forms an atypical zinc-binding domai n. Hs10 beta, but not the archaeal subunit, complemented an S. cerevis iae mutant (rpb10-Delta::HIS3) lacking Sc10 beta. Hs8 complemented a y east mutant (rpbB-Delta 1::LYS2) defective in the corresponding Sc8 su bunit, although with a strong thermosensitive phenotype. Interspecific complementation also occurred with Hs6 and with the corresponding Dm6 cDNA of Drosophila melanogaster. Hs6 cDNA and the Sp6 cDNA of S. pomb e are dosage-dependent suppressors of rpo21-4, a mutation generating a slowly growing yeast defective in the largest subunit of RNA polymera se II. Finally, a doubly chimeric S. cerevisiae strain bearing the Sp6 cDNA and the human Hs10 beta cDNA was also viable. No interspecific c omplementation was observed for the human hRPB25 (Hs5) homolog of the yeast ABC27 (Sc5) subunit.