[The nature of the emergence of His+-revertants in Salmonella typhimurium].

The His(-)-->His+ spontaneous reversion of the Salmonella typhimurium alleles hisD3052 and hisG46 was studied. The expected jackpot distribution of His+ revertants was not observed in the fluctuation tests. The experimental distributions were close to Poisson. It was also shown that the mean number of His+ reversion events and the mean number of revertants per plate were similar. These data demonstrate that the His+ reversion occurred under the influence of histidine starvation. At the same time, kanamycin resistant mutants had the jackpot distribution. Selection for His+ revertants did not increase the Kans-->Kanr mutations.