Virus-Specific Proteins Synthesized in Encephalomyocarditis Virus-Infected HeLa Cells

Abstract

The in vivo synthesis of encephalomyocarditis-specific proteins was studied by labeling the viral proteins with radioactive amino acids under conditions where host-protein synthesis was almost completely inhibited. To assure recovery of all proteins, intact cells were lysed in hot 1% sodium dodecyl sulfate. These lysates were analyzed by quantitative high-resolution electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. This technique allowed the detection and estimation of the molecular weight of 15 virus-specific polypeptides: A, 100,000; B, 90,000; C, 84,000; D, 75,000, D1, 65,000; E, 56,000; ε, 40,000; F, 38,000; α, 34,000; β, 30,000; γ, 23,000; G, 16,000; H, 12,000; I, 11,000; and δ, 9,000. Pulse-chase experiments, in conjunction with cyanogen bromide and tryptic mapping of the isolated polypeptides, indicate that at least three primary gene products (A,F,C), with a cumulative weight of about 220,000, are generated during translation of the RNA genome. Chains A and C then undergo post-translational cleavages, while F remains uncleaved. The proteins generated by the cleavage of A include all of the capsid chains (α, β, γ, δ, ε). Those generated by the cleavage of C include D and E. The chains α, β, γ, δ, E, F, G, H, I, with a cumulative molecular weight of about 230,000, are stable and are produced in about equimolar amounts. A model for the synthesis of, and a cleavage sequence that accounts for, all of the viral polypeptides is proposed.

• gel electrophoresis
• tryptic mapping
• cyanogen bromide mapping