Proteolytic processing of the proteins translated from the bottom component RNA of cowpea mosaic virus. The primary and secondary cleavage reactions.

The products of translation of cowpea mosaic virus B-RNA in rabbit reticulocyte lysates are proteolytically cleaved to form a specific set of proteins. The primary cleavage occurs as nascent peptide chains elongate to a size of about 150 kilodaltons yielding a 32K protein and, upon chain completion, a 170K protein. This cleavage reaction is inhibited by 3 mM iodoacetamide. The 170K protein, in turn, is cleaved to yield either of two pairs of proteins, a 110K and 60K pair or a 87K and 84K pair. The reaction for forming the 110K-60K pair is sensitive to dilution, indicating that a free factor is involved. The reaction for forming the 87K-84K pair, on the other hand, is not affected by diluting the lysate reaction mixture with buffer even to 200-fold, indicating that the reaction is autolytic. Formation of the 110K-60K pair, but not the 87K-84K pair, is inhibited by 2 mM zinc chloride. Translational mapping data indicate that the 87K and 60K proteins are derived from the NH2-terminal side of the 170K protein.