Molecular characterization of the CmbR activator-binding site in the metC–cysK promoter region in Lactococcus lactis

Abstract

ThemetC–cysKoperon involved in sulphur metabolism inLactococcus lactisis positively regulated by the LysR-type protein CmbR. Transcription from themetCpromoter is activated when concentrations of methionine and cysteine in the growth medium are low. ThemetCpromoter region contains two direct and three inverted repeats. Deletion analysis indicated that direct repeat 2 (DR2) is required for activation of themetCpromoter by CmbR. Gel mobility shift assays confirmed that CmbR binds to a 407 bp DNA fragment containing themetCpromoter. This binding was stimulated byO-acetyl-l-serine. Competition experiments with deletion variants of themetCpromoter showed that CmbR binding only occurred with fragments containing an intact DR2, confirming that DR2 is the CmbR binding site within themetCpromoter.