(argC) (argB) (argH) Promoter Operator Gene 1 Gene 2 Gene 3 RNA polymerase ->Transcription occurs a Repressor (argC) (argB) (argH) PromoterOperator Gene 1 Gene 2 Gene 3 RNA Corepressor polymerase Transcription blocked Repressor (b) 负控阻遏系统负控阻遏系统