Suppression of Amber Mutations of Bacteriophage T4 Gene 43 (DNA Polymerase) by Translational Ambiguity

Abstract

The growth properties of twelve different amber (am) mutants of bacteriophage T4 gene 43 (DNA polymerase) were examined by using nonpermissive (su-) as well as permissive (su+) Escherichia coli hosts. It was found that most of these mutants were measurably suppressed in su-hosts by translational ambiguity (misreading of codons during protein synthesis). The ability of these mutants to grow in response to this form of weak suppression probably means that the T4 gene 43 DNA polymerase can be effective in supporting productive DNA replication when it is supplied in small amounts. By similar criteria, studies with other phage mutants suggested that the products of T4 genes 62 (uncharacterized), 44 (uncharacterized), 42 (dCMP-hydroxymethylase), and 56 (dCTPase) are also effective in small amounts. Some T4 gene products, such as the product of gene 41 (uncharacterized), seem to be partially dispensable for phage growth since am mutants of such genes do propagate, although weakly, in streptomycinresistant su-hosts which appear to have lost the capacity to suppress am mutations by ambiguity.

Late effect of bacteriophage T4D on the permeability barrier of Escherichia coli

“…In a T4+ infection a comparison of the optical density at 490 nm (OD490) of resuspended VOL. 25,1978 a E. coli B was grown to 5.4 X 108 cells per ml.…”

“…The cation loss is apparent even when infection is at 30°C (data not shown) where [t]infected cells have even less tendency to lyse than at 370C (22). Since it was possible that the t amber mutant was "leaky," its behavior was tested on a strain of cells (E. coli B Strr) that exhibits low ribosomal ambiguity (16,25,38). Results similar to those of Fig.…”

“…Both E. coli B, nonpermissive for T4 amber (am) mutants, and E. coli CR63, permissive for T4 am mutants, have been described (47). E. coli B Str', a streptomycin-resistant strain, was obtained from S. Hattman; we have confirmed its low ribosomal ambiguity by using a T4 gene 43 amber mutant according to Karam and O'Donnell (25). E. coli CR63 (A) was obtained from A. Campbell.…”

Analysis of expression of the rII gene function of bacteriophage T4

“…Some of the E. coli K-12 derivatives used had been cured of A phage by heteroimmune superinfection with 21hyb2 phage and relysogenized with a wild-type strain of X(A++). The properties of these and other bacterial strains used have been described (14,15).…”

“…Media and growth conditions. The liquid and solid media that were used in most experiments were as described previously (14,15). The effects of Mg2+ on the rII mutant phenotypes were studied by using the growth conditions described by Garen (8) with the following modifications.…”