Summary: The sensitivities of lon strains of Escherichia coli to the filament inducing agents nalidixic acid, gentian violet, crystal violet and penicillin were examined. The strains used included those in which the lon gene is suppressed by sul, exr and rec as well as strains in which the Lon phenotype is expressed. The sensitivity of the bacteria to agents which act on DNA was reduced when lon was suppressed, but the extent of the decrease in sensitivity was dependent on the mechanism by which suppression was effected. Sensitivity to penicillin, on the other hand, was reduced only in the sul strain and by a mechanism which appears to be independent of the direct suppression of lon. A model to account for these results indicates possible sites at which the lon, sul, exrA and recA genes are expressed.
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