Bacteriophage T4 head morphogenesis: V. The role of DNA synthesis in maturation of an intermediate in head assembly

On the basis of metabolic-inhibitor studies it was found that maturation of T4 head intermediates, which had accumulated in tsC9 (gene 49) mutant infected cells, was apparently dependent on continued DNA synthesis. This requirement for DNA synthesis in head maturation was confirmed by using a gene 43 mutant ( tsP36) blocked in the enzyme, T4 DNA polymerase. In temperature shift-up experiments with tsP36-infected cells it was found as previously reported ( Luftig and Ganz, 1972) that 300s particles accumulated when enzyme synthesis was halted. These latter structures appear identical to the gene 49-defective intermediates since, when isolated, they both: (i) had an average sedimentation coefficient of 310 ± 20s and a nucleoprotein density of 1.34 g/cc; (ii) had the major capsid polypeptide in a cleaved state; (iii) were quantitatively rescued (to a >50% level in 40 min) after the mutant-blocked function was recovered, and (iv) showed a reduced ability to convert to phage when an inhibitor of DNA synthesis such as fluorodeoxyuridine (FUdR) was added at the time the function was rescued. The maturation of rapidly labeled 300s wild-type (T4D +) head intermediates was also found to be sensitive to inhibitors of DNA synthesis. Upon isolation these heads had the same properties as the above gene 49 and gene 43 mutant-defective intermediates. This strongly suggests that DNA synthesis is a normal requirement for maturation of a T4 capsid intermediate, whose properties are defined above.