Regulatory mutations of the Pseudomonas plasmid alk regulon

Pseudomonas putida strains with plasmids carrying pleiotropic alk mutations gave rise to alkane-positive "revertants," which differ from wild type. Some had restricted ability to utilize alkane and primary alcohol growth substrates, and others could grow on undecane and dodecanol, which are not utilized by alk+ strains. These revertants showed altered responses to normal inducers of alkA+, alkB+, and alkC+ activities. Some revertants were constitutive for these activities. Constitutive mutants could also be isolated directly from wild type, but they appeared spontaneously at a frequency of less than 2 X 10(-8). Regulatory mutations of all three types, pleiotropic negative, altered inducer specificity, and constitutive, were tightly linked in transduction crosses with a polar alkB mutation. These results demonstrate that the IncP-2 plasmid alk gene cluster constitutes a regulon. They also permit the identification of at least one cistron whose gene product participates in inducer recognition and suggest that the alkABC regulon is not under simple repressor control.