Identification of a lactose-responsive element upstream of the promoter of Bacillus megaterium beta-galactosidase-encoding gene mbgA.

The Bacillus megaterium mbgA gene encodes a lactose-hydrolyzing beta-galactosidase. An AraC/XylS-type activator BgaR can activate mbgA transcription in response to lactose. In this report, we show by various deletion analyses and point mutagenesis analyses that an inverted repeat centered at position -60.5 relative to the mbgA transcriptional initiation site is the cis-acting element responsible for lactose induction of mbgA expression.