GENETIC INSTABILITY IN ESCHERICHIA COLI.

Schwartz, Norman M. (Yale University, New Haven, Conn.). Genetic instability in Escherichia coli. J. Bacteriol. 89:712-717. 1965.-Results obtained from a transductional analysis demonstrated that an extremely unstable reversion of lac(-) is a suppressor mutation. This mutation suppresses 2 of 22 different lac(-) alleles tested. Five different Hfr strains transferred the suppressor soon after mating and at low frequency. Acridine orange enhanced the segregation of lac(-) clones from the unstable suppressed mutant. Stable suppressed lac(-) clones were produced by the unstable suppressed mutant. Two such stable suppressors were transferred at high frequency and mapped at different chromosomal sites on the basis of time of entry data. One of the stable suppressed lac(-) mutants reverted to the unstable suppressed lac(-) state. It is proposed that the suppressor is carried on an extrachromosomal element. The differences in stability observed may reflect differences in the state of the suppressor-bearing element.