New class of conditional colicin-tolerant mutants.

A new class of temperature-dependent tol mutants of Escherichia coli expresses tolerance to colicins only after growth at higher temperatures. Colicin sensitivity or tolerance, acquired by growth at 30 or 41 C, respectively, is not lost upon incubation at the other temperature in the presence of chloramphenicol. The kinetics of conversion from sensitivity to tolerance and vice versa have been analyzed. In one instance, the tol VIII temperature-dependent phenotype was due to the modifying role of a str-r mutation on the suppression of a tol VIII amber mutant by the suppressor mutation suII. The bearing of the present findings on the role of the tol genes is discussed.