Purification and characterization of a major component from the cytoplasmic matrix of cultured murine L cells.

This study describes the purification and preliminary characterization of a 94 000 molecular weight protein (S-94) previously known only as a major band in SDS-polyacrylamide gels of total proteins from cultured murine cells. Native S-94 is a soluble constituent of the cytoplasm and sediments at 5.0 S in sucrose gradients, behavior compatible with that of a 94 000 molecular weight monomer. S-94 is purified more than 20-fold from the 100 000 X g supernatant of murine L or L1210 lymphoma cells by DEAE-Sephadex (A-50) chromatography in the presence of 2-mercaptoethanol followed by Sephadex G-200 chromatography in 8 M urea. The protein prepared by this procedure is extensively aggregated, but is essentially homogeneous by SDS-polyacrylamide gel electrophoresis. S-94 preparations from the two types of murine cells behave identically during the purification procedure and are presumed to be the same protein. It appears that these cells contain only one major protein of 94 000 molecular weight. Purified S-94 yields a distinctive pattern of fragments following CNBr degradation, including one peptide of 36 100 molecular weight. The amino acid composition is distinguished by being relatively rich in threonine, glycine and lysine, but poor in valine, leucine and tyrosine.