Extensive homology among the largest subunits of eukaryotic and prokaryotic RNA polymerases

We have determined the nucleotide sequence of two yeast RNA polymerase genes, RPO21 and RPO31, which encode the largest subunits of RNA polymerases II and III, respectively. The RPO21 and RPO31 sequences are homologous to each other, to the sequence of the largest subunit of E. coli RNA polymerase, and to sequences in the putative DNA-binding domain of E. coli DNA polymerase I. RPO21 has an unusual heptapeptide sequence tandemly repeated 26 times at its C-terminus; this sequence is conserved in the RNA polymerase II of higher eukaryotes and may play an important role in polymerase II-mediated transcription. Since eukaryotic and prokaryotic RNA polymerases appear to have evolved from a common ancestral polymerase, other features of the transcription process may also be evolutionarily conserved.