HIGH CONSERVATION OF SUBUNIT COMPOSITION OF RNA-POLYMERASE-I(A) BETWEEN YEAST AND MOUSE AND THE MOLECULAR-CLONING OF MOUSE RNA-POLYMERASE-I40-KDA SUBUNIT RPA40

Mouse RNA polymerase I (or A) was purified from an ascites cell line M H134 to virtual homogeneity using a novel purification procedure and e xamined for subunit composition. In marked contrast to older purificat ions that reported 5-8 subunits, polymerase I was found to have 11 sub units with remarkable correspondence to those of yeasts. The cDNA enco ding a 40-kDa subunit of this enzyme, designated RPA40, was isolated. It predicts a polypeptide of 355 amino acids (M(r), = 40,065) and is e ncoded by a single copy gene. Protein sequence analysis reveals that R PA40 is the homolog of yeast RPC40, having homology 60 alpha subunit o f Escherichia coli RNA polymerase, yeast RPB3, and human RPB33 RNA pol ymerase II subunits. The high conservation of this subunit among dista nt eukaryotes and different RNA polymerases suggests functional import ance of this protein as a core subunit.