Further Studies with Lipoamide Dehydrogenase Mutants of Escherichia coli k12

Abstract

The immunological properties of ten lipoamide dehydrogenase mutants of Escherichia coli were investigated with antiserum raised against purified lipoamide dehydrogenase. Seven mutants were CRM+ (cross-reacting material present) as they contained lipoamide dehydrogenase proteins exhibiting either complete or partial immunological identity with the wild-type protein. This indicates that at least seven of the mutations affect the lipoamide dehydrogenase structural gene ( lpd ). The remaining three mutants (CRM-) contained no detectable cross-reacting protein. None of the lpd mutations were sensitive to any of three different amber -suppressors. Genetic analysis by P1-transduction showed that all the lpd mutant sites were clustered very near the distal gene ( aceF ) of the ace region which specifies the dehydrogenase ( aceE ) and transacetylase ( aceF ) components of the pyruvate dehydrogenase multienzyme complex. Calculations based on the recombination frequency between an aceF mutant and the nearest lpd mutant site support the conclusion that apart from the possible presence of a regulatory element, the aceF and lpd genes are contiguous.