Yeast POL5 Is an Evolutionarily Conserved Regulator of rDNA Transcription Unrelated to Any Known DNA Polymerases

We show that yeast protein Yel055cp, which has been identified as the fifth essential DNA polymerase in Saccharomyces cerevisiae (POL5), is a member of a family of predicted rDNA transcription regulators (typified by human MYB-binding protein MYBBP1A), which are represented by a single ortholog in all animals, fungi and plants with sequenced genomes. These proteins are confidently predicted to have an entirely α-helical structure and are unrelated to the B class DNA polymerases, as claimed for yeast POL5, or any other known polymerases.