Analysis of T4 phage proteins. I. Conversion of precursor proteins into lower molecular weight peptides during normal capsid formation.

Radioisotopically labeled T4-proteins extracted from purified capsids and phage and from infected cells were separated by gel electrophoresis in the presence of sodium dodecyl sulfate and a reducing reagent. They were identified by autoradiography and by counting of the fractionated gels. Four major protein bands (F, A, D, and E) were detected in capsid and phage. These accounted for more than 90% of the total capsid protein and 70% of the phage protein (60% of the total capsid protein was in A-band). Coelectrophoresis of [(14)C]proteins from capsids and [(3)H]proteins from phage-infected cells indicated that the protein coded by gene 23 (P23) was a peptide chain approximately 25% longer than A-protein. Pulse-chase experiments combined with differential extraction indicated that conversion of P23 into A-protein and alteration of the protein coded by gene 22 (P22) appeared to be vital steps in formation of normal capsids. Mutations in several other genes known to prevent normal capsid formation inhibited conversion of P23 to A-protein and alteration of P22.