Cold-Sensitive Mutants of Bacteriophage φX174. II. Comparison of Two Cold-Sensitive Mutants

Abstract

Cold-sensitive bacteriophage φX174 mutants, another class of conditional lethals, were examined with regard to growth parameters, DNA synthesis, and particle properties. Two mutants, cs 70 and cs 82, were examined. Mutant cs 70 was eclipse defective, showing altered eclipse kinetics at permissive temperature (40 C) and failing entirely to eclipse at restrictive temperature (25 C). Mutant cs 70 replicated well at 25 C if allowed prior eclipse at 40 C. Mutant cs 82 had wild-type eclipse at both temperatures but was defective in single-strand synthesis at 25 C, which led to delayed progeny phage appearance, decreased progeny phage synthesis rate, and greatly reduced burst size. The cs 82 block could not be bypassed by temperature shift. Since complementation analysis of cs 70 and cs 82 was not feasible due to the unique properties of these mutants, those φX174 properties affected by the virus coat were examined as an index of a mutation in a coat protein gene. Mutant cs 70 had aberrant attachment kinetics at both 25 C and 40 C, evidence of a coat protein alteration. Mutant cs 70 also exhibited significantly decreased thermal stability, further evidence of an altered virus structure. Mutant cs 82 had increased thermal stability, but the difference was not sufficient to allow unequivocal assignment of this mutant to a coat protein gene. Both mutants had wild-type antiserum inactivation and host range, although cs 70 was subject to less of (low-level) plating restriction by endogenous F + factors.