A regulatory cascade in the induction of rhaBAD

J Mol Biol. 1993 Nov 5;234(1):87-98. doi: 10.1006/jmbi.1993.1565.


The RhaS and RhaR regulatory proteins are encoded in the Escherichia coli L-rhamnose gene cluster. We used complementation analysis and DNA mobility shift assays to show that RhaR is not the direct activator of the L-rhamnose catabolic operon, rhaBAD. An in-frame deletion of rhaS (rhaS-rhaR+) eliminated expression from the rhaBAD promoter, pBAD, while overexpression of rhaS greatly speeded the normally slow induction of transcription from pBAD. Expression from pBAD in a coupled transcription-translation assay was only detected when rhaS+ DNA was added to allow synthesis of RhaS protein. RhaS thus appears to be the direct L-rhamnose-specific activator of rhaBAD expression. Deletion mapping located the binding site for the L-rhamnose-specific regulator to a region overlapping position -70 relative to the rhaBAD transcription start site. Deletion mapping and DNA mobility shift assays located a CRP binding site just upstream from the binding site for the L-rhamnose-specific regulator. Quantitative primer extension analysis showed that induction of both the rhaBAD and rhaSR messages was unusually slow, requiring 40 to 50 minutes to reach a steady-state level. Induction of rhaBAD apparently involves a regulatory cascade in which RhaR first induces rhaSR expression, then RhaS accumulates and induces rhaBAD expression.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / physiology
  • Base Sequence
  • Carrier Proteins
  • Cyclic AMP Receptor Protein / metabolism
  • DNA Primers / chemistry
  • DNA, Bacterial / genetics
  • DNA-Binding Proteins / metabolism
  • DNA-Binding Proteins / physiology*
  • Escherichia coli Proteins*
  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial
  • Genes, Regulator*
  • Molecular Sequence Data
  • Operon*
  • Promoter Regions, Genetic
  • Rhamnose / metabolism*
  • Trans-Activators*
  • Transcription Factors / physiology*
  • Transcription, Genetic


  • Bacterial Proteins
  • Carrier Proteins
  • Cyclic AMP Receptor Protein
  • DNA Primers
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • RhaR protein, E coli
  • RhaS protein, E coli
  • Trans-Activators
  • Transcription Factors
  • Rhamnose