HOST-DEPENDENT SYNTHESIS OF ALTERED DEOXYCYTIDYLATE HYDROXYMETHYLASE AFTER INFECTION OF ESCHERICHIA COLI WITH CERTAIN AMBER MUTANTS OF BACTERIOPHAGE T4 ,

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Abstract
The amber mutants of bacteriophage T4 are conditional lethal mutants. Infection of nonpermissive hosts, such as E. coli B, is abortive, and in the case of infection with the mutants used in this work no active dCMP hydroxymethylase is formed, whereas other phage-initiated enzymes are made. Infection of three derivatives of E. coli K12 that permit replication of the mutants results in the forma-tion of enzymes that show differing degrees of temperature sensitivity. The enzymes formed after infection of the three permissive hosts with each of the four mutants (am B269, am N122, am N55, or am B21) were tested for relative heat stability. In any host certain differences were found in the stabilities of the enzyme formed after infection with dif-ferent mutants. A comparison of the relative temperature sensitivity of the enzyme induced by one mutant in the different hosts revealed host dependence with respect to the nature of the protein formed. The evidence presented is in accord with the hypothesis that the mutation in the phage genome gives rise to nonsense or unacceptable missense in E. coli B, and to acceptable missense in the permissive hosts.