Identification of a 100‐kDa protein associated with nuclear ribonuclease P activity in Schizosaccharomyces pombe

Ribonuclease P from the fission yeast Schizosaccharomyces pombe has been purified to apparent homogeneity. A purification of 23000‐fold was achieved by four fractionation steps with DEAE‐cellulose chromatography, phosphocellulose chromatography, glycerol‐gradient fractionation and finally tRNA‐affinity chromatography. A 100‐kDa protein was present in the most pure preparations in amounts approximately stoichiometric with the previously identified RNA components of the enzyme, K1‐RNA and K2‐RNA [Krupp, G., Cherayil, B., Frendeway, D., Nishikawa, S. & Söll, D. (1986) EMBO J. 5 , 1697–1703]. A cross‐linking experiment utilizing a 4‐thiouridine‐substituted precursor tRNA demonstrated that the 100‐kDa protein interacts with the ribonuclease P substrate in a specific fashion. We therefore conclude that the protein component of S. pombe ribonuclease P is a 100‐kDa protein.