RNA polymerase mutant able to express in vivo and in vitro the lactose operon in the absence of the cAMP-CRP complex.

By genetic analysis, we have localized a new mutation, isolated from rho-crp background, responsible for a carbohydrate-positive phenotype. The mutation maps in the rpoB gene coding for the beta-subunit of Escherichia coli RNA polymerase. Using reverse transcriptase analysis of transcripts obtained in vivo and transcription assays in vitro, we have shown that this altered RNA polymerase can efficiently initiate the transcription of the lactose operon in the absence of the cAMP-CRP complex both in vivo and in vitro.