Four subunits of Schizosaccharomyces pombe RNA polymerases I-III shared by all three enzymes (Rpb5, Rpb8, Rpb10 and Rpc10 [Rpb12]) have been overexpressed in Escherichia coli expression vectors pQE or pET as hexahistidine fusions. The recombinant proteins have been purified to near homogeneity using metal-chelate affinity chromatography and gel filtration. Homogeneity and identity of the purified protein preparations was demonstrated by denaturing polyacrylamide gel electrophoresis and TOF-MALDI mass spectrometry. The proteins were obtained in large amounts, and their preparations are currently in use for monoclonal antibody production and physico-chemical studies of these individual components of eukaryotic transcription enzymes.