[Some genetic features of adaptive mutation].

The research based on the Escherichia coli FC40 showed that adaptive mutations required the enzymes of RecBCD recombination pathway and some unknown proteins of SOS response, and the mutation spectrum of lac+ revertants is single-base deletions in the small mononucleotide repeats. Some evidence showed that the revertants with adaptive mutations partly come from one (or some) subset of transient hypermutable subpopulation of cells, in which high frequently losing of transposons and genome-wide mutations were observed. It was suggested that this kind of transient hypermutability may be due to the transient deficient activity of mismatch repair (MMR) system, or a defective epsilon unit of DNA polymerase III generated by mistranslation.

[The occurrence of actual F factor transfer during the stationary-phase mutation in Escherichia coli FC40].

The experiment of adaptive mutation was performed by using Escherichia coli GM133 rif(r) as test cells and HB214 str(r) as scavenger cells. Transfer frequency between GM133 and HB214 was estimated,based on the number of revertants appeared on the selective plates when GM133 were killed by addition of M9 selective medium containing 100 microg/mL of streptomycin at different time. After 30 minutes the cells of GM133 and HB214 were mixed,the estimated transfer frequency was about 0.