To construct a regulatory network, it is necessary to identify every transcription factors binding to a specific promoter.In this work, we developed a de nove designed genetic circuit for the screening of repressor proteins in Escherichia coli.This biosensor circuit could convert the repression input of a certain regulator into a visul output displayed by the xylE-neo reporter cassette (Fig.1).After examining the sensitivity and bias of this biosensor circuit, the scbA (encoding the quorum sensing signal SCB1 synthetase) promoter (scbAp) of Streptomyces coelicolor was used as a target to identify corresponding regulators.