SUMMARY: Galactokinaseless mutants of are, in general, phenotypically constitutive for the remaining enzymes of the galactose pathway, 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, W3092A, also produces a constitutive concentration of enzyme after confluent growth on solid medium and continues 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 W3092A. It does not occur in other inducible strains, including galactose-fermenting revertants of W3092A, nor in W3092A 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 prevented by an inhibitor of induction of the galactose enzymes, methyl-β--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 W3092A (A character) was shown to be independent of the mutation to kinaseless, since other kinaseless mutants derived from a galactose-fermenting revertant of W3092A still carried the A character.


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