Characterization of the lys2 gene of Acremonium chrysogenum encoding a functional α-aminoadipate activating and reducing enzyme

Abstract.

A 5.2-kb NotI DNA fragment isolated from a genomic library of Acremonium chrysogenum by hybridization with a probe internal to the Penicillium chrysogenum lys2 gene, was able to complement an α-aminoadipate reductase-deficient mutant of P. chrysogenum (lysine auxotroph L^–G^–). Enzyme assays showed that the α-aminoadipate reductase activity was restored in all the transformants tested. The lys2-encoded enzyme catalyzed both the activation and reduction of α-aminoadipic acid to its semialdehyde, as shown by reaction of the product with p-dimethylaminobenzaldehyde. The reaction required NADPH, and was not observed in the presence of NADH. Sequence analysis revealed that the gene encodes a protein with relatively high similarity to members of the superfamily of acyladenylate-forming enzymes. The Lys2 protein contained all nine motifs that are conserved in the adenylating domain of this enzyme family, a peptidyl carrier domain, and a reduction domain. In addition, a new NADP-binding motif located at the N-terminus of the reduction domain that may form a Rossmann-like βαβ-fold has been identified and found to be shared by all known Lys2 proteins. The lys2 gene was mapped to chromosome I (2.2 Mb, the smallest chromosome) of A. chrysogenum C10 (the chromosome that contains the "late" cephalosporin cluster) and is transcribed as a monocistronic 4.5-kb mRNA although at relatively low levels compared with the β-actin gene.