Design of a system of conditional lethal mutations (tab/k/com) affecting protein-protein interactions in bacteriophage T4-infected Escherichia coli

The re-direction of host-cell machinery to virus-specific functions, by the physical interaction between viral proteins and pre-existing host proteins, may be a mechanism commonly exploited in virus infection. We argue that the formation of a hybrid complex between an Escherichia coli protein and bacteriophage T4 protein controls the assembly of T4 capsid precursors into ordered structures. This early step in assembly can be blocked either by a mutation in T4 gene 31 (Laemmli et al., 1970), or by a bacterial mutation (groE, tabB) (Georgopoulos et al., 1972; Coppo et al., 1973). We show that this step can also be blocked by the interaction of bacterial mutations (tabB^k, tabB^com) and viral mutations k^B and com⁸); com^B mutations map in T4 gene 31, while k^B mutations map in either gene 31 or 23. Many k⁸ mutants are also temperature-sensitive. Phage T4 head assembly is blocked when tabB^k (or tabB^com) are infected with T4k^B (or com^B), but not when the bacterial mutant is infected with T4 wild-type, or when tab⁺ cells are infected with k^B (or com^B). We interpret this phenomenon as a case of negative complementation between altered host and viral subunits of a hybrid complex and illustrate this idea with the experiments described in the text. We describe a technique by which tabB mutants can be efficiently and specifically selected with k^B (or com^B) T4 mutants. Since many k^B mutants are temperature-sensitive, temperature-sensitive mutants in other genes also may have latent k properties, and may be used for the isolation of new tab bacterial mutants, identifying other interactions between T4 and E. coli proteins.