phage 11 was induced to replicate by treatment of lysogens with mitomycin C. Lysis was complete in 80 min at 37 °C in complete synthetic medium. Labelling with -[H]lysine showed a stimulation of protein synthesis during phage replication, followed after 30 min by shut-down of host protein synthesis while virion protein synthesis continued. The synthesis of approximately 16 virus-specific proteins was detected during replication, with seven of these recovered in purified virions after lysis. The remainder appeared to be synthesized earlier in phage replication and thus may represent precursors of virion proteins, or regulatory proteins, or enzymes associated with phage replication. Protein synthesis during replication of three suppressible morphological (head, tail) mutants of phage 11 did not differ significantly from that seen in the wild-type lysogen, indicating that the mutation in each case affected a protein whose synthesis was not detectable, or which was synthesized but did not fulfil its role in virion maturation or assembly. However, in a suppressible ‘early’ mutant which did not lyse when treated with mitomycin C, the synthesis of the ‘late’ (virion) proteins (with one exception) did not occur. ‘Early’ proteins were apparently made normally in this mutant, and there was no shut-down of host protein synthesis. This mutant phage presumably encodes a defective ‘early’ protein involved in the regulation of replication, or a key precursor polypeptide of ‘late’ protein synthesis. The morphological mutants provided a means to analyse and tentatively to allocate six of the virion proteins to head or tail/baseplate structures.


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