Cold-sensitive mutants of bacteriophage phi x174. II. Comparison of two cold-sensitive mutants

Cold-sensitive bacteriophage phiX174 mutants, another class of conditional lethals, were examined with regard to growth parameters, DNA synthesis, and particle properties. Two mutants, cs70 and cs82, were examined. Mutant cs70 was eclipse defective, showing altered eclipse kinetics at permissive temperature (40 C) and failing entirely to eclipse at restrictive temperature (25 C). Mutant cs70 replicated well at 25 C if allowed prior eclipse at 40 C. Mutant cs82 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 cs82 block could not be bypassed by temperature shift. Since complementation analysis of cs70 and cs82 was not feasible due to the unique properties of these mutants, those phiX174 properties affected by the virus coat were examined as an index of a mutation in a coat protein gene. Mutant cs70 had aberrant attachment kinetics at both 25 C and 40 C, evidence of a coat protein alteration. Mutant cs70 also exhibited significantly decreased thermal stability, further evidence of an altered virus structure. Mutant cs82 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 cs70 was subject to less of (low-level) plating restriction by endogenous F(+) factors.