[Cloning and sequence analysis of aspartokinase genes from Corynebacterium crenatum]

Aspartokinase genes (ask) from wild-type Corynebacterium crenatum AS1.542 and an AEC-resistant mutant Corynebacterium crenatum CD945 were cloned and sequenced. Analysis of ask sequence shows a exchange in a single base pair at position 1199 from T to C, leading to an amino acid change in the beta subunit of Aspartokinase. Leu80 in the wild-type is converted to Pro80 in the feedback-resistant enzyme. The substitution is located in ACT domain, a region regulated by concentration of lysine. The ORF sequence of ask from C. crenatum AS 1.542 shows homologies of 97.23%, 97.55% and 97.62% to those from C. glutamicum, C. flavum and B. lactofermentum. And the amino acid sequence deduced from ORF displays homologies of 99.76%, 99.52% and 99.76%, respectively. But there is much variation in the upstream sequence of C. crenatum AS 1.542 ask promoter compared to those from other Corynebacteria.