The coat protein subunits of potato virus X and white clover mosaic virus, a comparison of methods for determining their molecular weights and some in situ degradation products of potato virus X protein

The molecular weight of potato virus X (PVX) coat protein subunit was determined to be 27,600 by SDS-polyacrylamide gel electrophoresis; 27,000 by gel chromatography in 0.1% SDS; 26,500 by gel chromatography in 6 M guanidine hydrochloride, and 26,800 by chemical analyses. Partial proteolysis, occurring after storage of some virus preparations at 4 o for more than 2 weeks, and presumably due to the action of a contaminating plant protease(s), is possibly responsible for the discrepancy between the earlier reported value of 22,300 and the presently determined values for the molecular weight of the PVX-protein of about 27,000. In addition to the in situ , partial degradation of PVX coat protein caused occasionally by a plant protease(s), it was found, in extension of an earlier report, that trypsin causes the cleavage in situ from PVX-protein of a specific peptide containing 24 amino acid residues. The molecular weight of white clover mosaic virus (WCMV) coat protein subunit was also determined by both SDS-polyacrylamide gel electrophoresis and gel chromatography in 6 M guanidine hydrochloride and the values obtained were identical—23,500.