Polyacrylamide gel electrophoresis of the virus-specific proteins synthesized in vivo upon infection of E. coli with phage AMS21 2 yields three main fractions designated as proteins I, II, and III, of which protein III is coat protein. Experimerits with "amber" mutants indicate that protein JI is a viral RNA synlthetase, whereas protein I12 ' is a "maturation" protein.4 Translation of the RNA of coliphages by cell-free systems of E. coli gives rise to coat and other virus-specific proteins.5-8 Two of these proteins have been characterized as RNA synthetase and coat protein.8 The involvement of formylmethionine in initiation of coat protein synthesis9' 10 raises the question whether other virus-specific proteins are similarly initiated. There are some indications that this is the case.9' 11 The present work was undertaken in order (a) to further characterize the proteins formed upon translation of the MiS2 genome in vitro, and (b) to determine whether formylmethionine is the chain initiator of proteins other than coat. For characterization of the proteins synthesized in vitro, the C'4-labeled proteins formed by a cell-free E. coli system with i\1S2 RNA as messenger were coelectrophoresed with H3-labeled proteins produced by 1VIS2-infected, actinomycin-treated E. coli spheroplasts. The in vivo and in vitro proteins I and III were qualitatively identical but the in vitro system produced protein II to a much lesser extent, if at all. Moreover, the presence of one or more peaks, with a mobility intermediate between that of proteins II and III, suggested that unfinished or degraded peptides had been formed. In order to determine whether formylmethionine is involved in the initiation of both coat protein and protein I, in vitro incubations were conducted with H'-formyltetrahydrofolic acid and C'4-methionine, and the proteins isolated by polyacrylamide gel electrophoresis. The two proteins contained HI

Aided by grants AM-01845, AM-08953, and FR,05399 from the National Institutes of Health, U.S. Public Health Service, the Jane Coffin Childs Fund for Medical Research, and E. I. du Pont de Nemours and Co., Inc.

Peer reviewed