Der Einfluss von Suppressor-Gen-Mutation und intragenischer Reversion auf Mutationsorte vom 0°-Typ

Two classes of partial revertants of 0⁰-type mutants in the pyruvate dehydrogenase system ofEscherichia coli K 12 could be distinguished enzymatically and genetically. In one class of these strains the second mutation has occurred at or near the primary 0⁰ site. The partial revertants of this class synthesize a pyruvate dehydrogenase complex containing a defective carboxylase component. The strains of the other class proved to be suppressed 0⁰-type mutants,the second mutation having occurred outside the acetate locus on the E. coli chromosome. One of the suppressor alleles was found to be specific for a certain 0⁰ site; it did not act on another genetically distinguishable 0⁰ site nor on any of the tested mutant sites in the pyruvate dehydrogenase genes. The suppressed 0⁰ type strains synthesize only small amounts (about 1/50 of wild type) of pyruvate dehydrogenase with a carboxylase component which so far could not be distinguished from the wild type carboxylase. In addition, the suppressor gene mutants produce a partial complex of the pyruvate dehydrogenase which lacks the carboxylase component. It is not yet known whether or not this situation represents a disproportional synthesis of the constituent enzymes of the pyruvate dehydrogenase complex, i.e., production of smaller amounts of the carboxylase than required for the formation of the enzyme complex.