Viral and bacterial protein syntheses in MS2-infected Escherichia coli cells

Protein synthesis in Escherichia coli cells infected with the RNA bacteriophage MS2 was studied by a variety of techniques. Both β-galactosidase synthesis in the presence of an inducer and total protein synthesis, as measured by uptake of labeled amino acids into hot trichloroacetic acid-insoluble materials, were gradually reduced during the progress of infection. Electrophoresis on polyacrylamide gels of the [ 14C]phenylalanine-labeled proteins synthesized in MS2-infected cells showed that host protein synthesis decreased during the progress of infection, whereas synthesis of the viral coat protein increased gradually until it accounted for 30 to 40% of the total protein synthesized. The reduction of the synthesis of host proteins by infection was also examined using MU9, an amber mutant of MS2 which is unable to direct the synthesis of coat protein. Although cells infected with MU9 did not lyse, the synthesis of β-galactosidase as well as the total uptake of labeled amino acids was reduced as much as (or more than) in cells infected with wild-type MS2. Polyacrylamide gel electrophoresis of proteins synthesized in MU9-infected cells showed that the synthesis of host proteins was greatly reduced. In addition, two protein peaks were revealed which corresponded, in mobility, to MS2-specific RNA synthetase and “maturation” protein, respectively. Possible mechanisms for the inhibition of host-protein synthesis by MS2 infection are discussed.