Peptide mapping of phage Qβ proteins using cell-free synthesis

Abstract

Of the four proteins specified by the RNA of phage Qβ, three can be synthesized in a cell-free system in sufficient amounts to allow further analysis. These are coat protein (CP), read-through protein (A′), and replicase subunit (R). Arginine and lysine labeling was used to obtain the respective fingerprint patterns after tryptic digestion of the isolated products of cell-free synthesis. It was found that the CP patterns are contained in the A′ patterns. This is consistent with the notion that A′ is the read-through product of the coat gene. R shows complex patterns of about 20 lysine and 30 arginine peptides. Using a double labeling technique, methionine, cysteine, and histidine containing R peptides have been identified. By pulse-chase experiments information on the relative position of arginine, lysine, and histidine peptides of R could be obtained. The formylated and deformylated N-terminal peptides could be tentatively identified among the lysine peptides.