Mechanisms of negative control of transcription

(a) Effect of inducer Repressor protein DNA— Allosteric domain binding / No domain transcription Promoter Operator Gene Binding of repressor pro— tein blocks transcription by negative regulation. (b) Effect of corepressor Repressor protein Corepressor No transcription Promoter Operator Gene Binding of repressor— corepressor complex blocks transcription by negative regulation. Repressor protein Inducer RNA polymerase i Binding of inducer molecule ‘ to repressor protein allows transcription. 6 Repressor protein 0 RNA polymerase " Transcription With corepressor absent, repressor does not bind, allowing tran- scription.