[Episome stability in Escherichia coli K-12].

Arg+ and trp+ carrying episomes which have markedly different spontaneous efficiency of elimination, were obtained in experiments with AB673 and KL99 Escherichia coli donor strains. The level of episome maintenance is the result of mutation (deletion, insertion) that occurred in episomes during their formation. Differences in the efficiency of spontaneous elimination are independent of the origin of the donor strain used. The rate of loss of stably maintained episomes is not enhanced significantly by exposure of cells to AO. According to molecular characteristics, the episome demonstrating stable maintenance has a lower molecular mass than that of unstable maintenance.