EFFECT OF DIFFERENT LEVELS OF ASPARTOKINASE ON THE LYSINE PRODUCTION BY CORYNEBACTERIUM-LACTOFERMENTUM

A 2.9-kb SacI fragment containing the ask-asd operon, encoding asparto kinase and aspartate-semialdehyde dehydrogenase, was cloned from an am inoethylcysteine-resistant, lysine-producing Corynebacterium lactoferm entum strain. Enzymatic analysis showed that the aspartokinase (ASK) a ctivity was completely resistant to inhibition by mixtures of lysine a nd threonine. Comparison of the deduced amino acid sequence of the bet a subunit of the ask gene showed three amino acid residue changes with ask genes encoding wild-type, feedback-sensitive enzymes. Three C. la ctofermentum. turn strains, one being asp arte kinase-negative, one ca rrying two ask genes on the chromosome and one having a sixfold higher specific ASK activity than the parental strain, were constructed by t ransconjugation and electroporation, and used to analyse the role of A SK in the lysine production by C. lactofermentum. The results indicate that, in this study, feed-back-resistant ASK is necessary for high-le vel lysine production, but dispensable for lysine and diaminopimelate synthesis required for cell growth.