Bacteriophage T4 bypass31 mutations that make gene 31 nonessential for bacteriophage T4 replication: isolation and characterization

Abstract

T4 bacteriophage mutants called bypass31 (byp3l) that specifically suppress gene 31 amber mutations have been isolated and characterized. The mechanism by which the byp31 mutation, byp31-1, suppresses gene 31 nonsense mutations does not involve synthesis of gp3l or of a particular gp3l fragment; furthermore, the byp31 allele suppresses all nonsense mutations in gene 31 that have been tested. We detect no unusual properties among the T4 particles made in su-cells by the T4amN54byp31-1 double mutant. These virions, made in the absence of gp31, show normal heat sensitivity, normal sensitivity to osmotic shock, and normal morphology. Specific different gene 31 missense mutants are able to form plaques with high efficiencies on the following two types of host defective cells: (i) Escherichia coli groEL (Tilly et al., Proc. NatI. Acad. Sci. U.S.A. 78:1629-1633, 1981) mutants that block T4 capsid assembly and (ii) E. coli rho mutants in which T4+ heads are assembled, but in which tail production and DNA synthesis are blocked. (Note that not all rho mutants block T4 production [G.

Bacteriophage T4 bypass31 mutations that make gene 31 nonessential for bacteriophage T4 replication: mapping bypass31 mutations by UV rescue experiments

“…The accompanying paper (9) proposes the hypothesis that the T4 protein, gp3l, and the host protein, GroEL, are both required to carry out a single function in T4 capsid assembly.…”

“…In the accompanying paper, Simon and Randolph (9) describe a mutation of bacteriophage T4D, bypass31-1 (byp31-1), with two phenotypic characteristics that distinguish it from the wild type: (i) the normally required gene 31 product is dispensable, i.e., the mutant has the bypass 31 phenotype; and (ii) in contrast to wild-type T4, it can multiply in the hdB3-1 (herein referred to simply as B3-1) (8) and groEL defective strains of Escherichia coli. Thus the normal T4 host range has, with this mutation, been extended to include such strains.…”

“…The byp31-1 mutant of T4D used here was derived from the byp31-1 isolate described in the accompanying paper (9). The original strain, which carried an r mutation in addition to the bypass, was exposed to UV radiation at a dose of approximately 100 phage-lethal hits (PLH) and then crossed, in the amber-permissive host CR63, to the gene 23 doubleamber mutant amHllamE1236 (see map in Fig.…”