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A strain of Escherichia coli, CP 790302, severely restricts the growth of wild-type bacteriophage T4. In broth culture, most infections of single cells are abortive, although a few infected cells exhibit reduced burst sizes. In contrast, bacteriophage T4 mutants impaired in the ability to modify valyl-tRNA synthetase develop normally on this strain. Biochemical evidence indicates that the phage-modified valyl-tRNA synthetase in CP 790302 is different from that previously described. Although the enzyme is able to support normal protein synthesis, a disproportionate amount of phage structural protein (serum blocking power) fails to mature into particles of the appropriate density. The results with host strain CP 790302 are consistent with either a gratuitous inhibition of phage assembly by faulty modification or abrogation of an unknown role that valyl-tRNA synthetase might normally play in viral assembly.

Escherichia coli cells with plasmids bearing the valS gene were constructed from the Clark-Carbon collection. Their increased valyl-tRNA synthetase (EC 6.1.1.9) activity was not matched by commensurate production of a modifying peptide during T4 infection. Thus, phage vs gene expression is set to modify the normal amount of valyl-tRNA synthetase activity.