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SUMMARY Galactokinaseless mutants of Escherichia coli are, in general, pheno- typically constitutive for the remaining enzymes of the galactose path- way, a phenomenon which has been attributed to internal induction (Jordan, Yarmolinsky & Kalckar, 1962). One exceptional, kinaseless, mutant, though constitutive during stationary phase, is inducible during logarithmic growth. This mutant, w3092~, also produces a constitutive concentration of enzyme after confluent growth on solid medium and con- tinues to do so even after 3-5 generations of subsequent logarithmic growth in liquid medium. This effect of growth on solid medium is peculiar to ~3092~. It does not occur in other inducible strains, including galactose- fermenting revertants of w3092~, nor in ~3092~ itself grown as isolated colonies. Even in confluently grown organisms it is lost after storage at 4" for several days. In each case high degrees of enzyme synthesis can be pre- vented by an inhibitor of induction of the galactose enzymes, methyl- P-u-thiogalactoside, and are therefore attributed to internal induction. Though the enzyme concentrations decrease rapidly when the cultures resume logarithmic growth after stationary phase, high concentrations may persist up to the fifth generation after confluent growth on solid medium and then decline to reach the basal level only after the 12th generation. The inducibility of ~3092~ (A character) was shown to be inde- pendent of the mutation to kinaseless, since other kinaseless mutants derived from a galactose-fermenting revertant of ~3092~ still carried the A character.

Control of Internal Induction of Galactose Pathway Enzymes in an Escherichia coli Mutant