Abstract
ABSTRACT T4 phage completely defective in both gene 30 (DNA ligase) and the rll gene (function unknown) require at least normal levels of host-derived DNA ligase (E. coli lig gene) for growth. Viable E. coli mutant strains that harbor less than 5% of the wild-type level of bacterial ligase do not support growth of T4 doubly defective in genes 30 and rll (T4 30- rll- mutants). We describe here two classes of secondary phage mutations that permit the growth of T4 30- rll- phage on ligase-defective hosts. One class mapped in T4 gene su30 (KRYLO1V9 72) and improved T4 30- rll- phage growth on all E. coli strains, but to varying degrees that depended on levels of residual host ligase. Another class mapped in T4 gene 32 (heliz-destabilizing protein) and improved growth specifically on a host carrying the lig2 mutation, but not on a host carrying another lig- lesion (lig4). Two conclusions are drawn from the work: (1) the rde of DNA ligase in essential DNA metabolic processes in T4-infected E. coli is catalytic rather than stoichiometric, and (2) the E. coli DNA ligase is capable of specific functional interactions with components of the T4 DNA replication and/or repair apparatus.
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