Regulation of protein synthesis directed by coliphage MS2 RNA: I. Phage protein and RNA synthesis in cells infected with suppressible mutants

Abstract

In actinomycin-treated Escherichia coli infected with coliphage MS2 three phage-specific proteins have been detected after acrylamide gel electrophoresia. These proteins have been identified by the use of Suppressible mutants of MS2 as the phage coat protein, “maturation” or assembly protein and RNA synthetase. In MS2-infected cells RNA synthetase appeared before the other two proteins were detectable. All three proteins then increased, but the synthesis of maturation protein and RNA synthetase rapidly declined between 30 and 40 minutes post-infection, whereas the synthesis of coat protein continued at a high rate throughout the infectious cycle. The synthesis of phage RNA paralleled that of the RNA synthetase and maturation protein. Non-permissive cells infected with suppressible RNA synthetase mutants made no detectable phage proteins. Cells infected with maturation protein mutants showed a normal pattern of coat protein and RNA synthetase formation. Infection with a coat protein mutant resulted in a greater than normal rate of formation of RNA synthetase and maturation protein relative to the amount of phage RNA, and a higher percentage of each of these proteins was made late in infection compared to the situation in MS2-infected cells. However, the increase of these proteins was not co-ordinate: RNA synthetase formation increased more than the synthesis of maturation protein. In cells doubly infected with a maturation protein mutant and a coat protein mutant the derepression of synthetase and maturation protein seen in cells singly infected with the coat mutant was largely reversed. Our major conclusion is that the coat protein of MS2 serves as a repressor of the synthesis of maturation protein and RNA synthetase.