Possible involvement of the lysine ε-aminotransferase gene (lat) in the expression of the genes encoding ACV synthetase (pcbAB) and isopenicillin N synthase (pcbC) in Streptomyces clavuligerus

摘要

Streptomyces clavuligerus produces the β-lactam antibiotics penicillin N, O-carbamoyldeacetycelcephalosporin C and cephamycin C. We characterized a wild-type DNA region which restores antibiotic formation to a mutant strain named NP1, previously shown to exhibit depressed activities for two early enzymes of cephalosporin synthesis, δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS) and isopenicillin N synthase (IPNS). L-Lysine ε-aminotransferase (LAT) assays and α-AAA feeding experiments suggested that strain NP1 is a lat mutant. NP1 recovered LAT, ACVS and IPNS activities when transformed with the cloned region. DNA sequencing showed that this region encodes the entire LAT gene (lat), required for the conversion of L-lysine to the β-lactam precursor L-α-aminoadipic acid (α-AAA), as well as the upstream half of the ACVS gene (pcbAB). The activities of ACVS and IPNS appear to depend upon LAT expression. Gene fusions constructed to investigate promoter activities in the cloned region support a model of interdependence in the expression of the genes for LAT, ACVS and IPNS (pcbC).