SUMMARY: Mutants of 8602 were isolated which, unlike the wild-type strain, utilized butyramide as a growth substrate. One group produced amidases with altered substrate specificities, indicating that the mutations may be in the amidase structural gene. The second group of butyramide-utilizing mutants produced wild-type enzyme and were all constitutive. It was concluded that such mutants possessed mutations in an amidase regulator gene which allowed them to synthesize large amounts of amidase in the presence of butyramide.

Induction of amidase synthesis by -acetylacetamide in the wild-type strain was repressed in a competitive manner by butyramide and other amide analogues, e.g. cyanoacetamide. The constitutive mutant c11, which could not utilize butyramide for growth, was subject to severe repression of amidase synthesis by butyramide and cyanoacetamide. The regulator mutants which were able to grow on butyramide were all less sensitive to repression by butyramide. Mutant cb 2, a butyramide-utilizing regulator mutant, was relatively insensitive to repression of amidase synthesis by cyanoacetamide whereas strain b6, a butyramide-utilizing mutant producing an altered enzyme, was as sensitive to repression by cyanoacetamide as its parent strain the constitutive mutant c11. The contribution of mutations in structural and regulator genes to utilization of novel growth substrates is discussed.


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