DNA looping and unlooping by AraC protein

  title={DNA looping and unlooping by AraC protein},
  author={RB Lobell and RF Schleif},
  pages={528 - 532}
Expression of the L-arabinose BAD operon in Escherichia coli is regulated by AraC protein which acts both positively in the presence of arabinose to induce transcription and negatively in the absence of arabinose to repress transcription. The repression of the araBAD promoter is mediated by DNA looping between AraC protein bound at two sites near the promoter separated by 210 base pairs, araI and araO2. In vivo and in vitro experiments presented here show that an AraC dimer, with binding to… 
The role of rigidity in DNA looping-unlooping by AraC.
Results are consistent with the light switch mechanism for the action of AraC, refine the model, and extend the range of experimental tests to which it has been subjected.
Apo-AraC actively seeks to loop.
These results demonstrate that apo-AraC possesses an intrinsic looping preference that is eliminated by the presence of arabinose, and developed a method for the accurate determination of the relative affinities of AraC for the DNA half-sites araI1, aRAI2, and araO2 and non-specific DNA.
Helical Behavior of the Interdomain Linker of the Escherichia coli AraC Protein.
Evidence is provided that, in shifting from the repressing to the inducing state, the behavior of interdomain linker shifts from that of an alpha-helix to that of a flexible nonhelical form, providing a plausible mechanism for arabinose to control the repressed-inducing state of AraC protein.
In vivo induction kinetics of the arabinose promoters in Escherichia coli
The induction response of the wild-type arabinose operons from their native chromosomal locations is characterized by primer extension analysis and the relative levels of inducibility in wild- type cells of araBAD, araFGH, and araE are determined to be 6.5, 5, and 1, respectively.
Constitutive Mutations in the Escherichia coli AraC Protein
Fluorescence, circular dichroism, and cysteine reactivity measurements show that the constitutive mutations in the core of the dimerization domain lead to a weakening of the support for the arms and reduce the stability of the minus-arabinose arm structure.
Sequence elements in the Escherichia coli araFGH promoter
The effects of 11 mutations within the DNA region thought to bind the cyclic AMP receptor protein correlate well with the CRP consensus binding sequence and confirm that this region is responsible for cyclicAMP regulation.
Repression of the araBAD promoter from araO1.
Heterodimers reveal that two arabinose molecules are required for the normal arabinose response of AraC.
It is found that the normal arabinose response of AraC requires the binding of twoArabinose molecules, which provides additional constraints on mechanistic models for the action of Ara C.
In Vitro Repression of the gal Promoters by GalR and HU Depends on the Proper Helical Phasing of the Two Operators*
It is concluded that the observed in vitro repression of gal transcription in vitro is mediated by DNA looping and the in vitro conditions reflect the in vivo situation.


Alternative DNA loops regulate the arabinose operon in Escherichia coli.
The results of in vivo dimethyl sulfate "footprinting" experiments to monitor occupancy of the three AraC sites and measurements of activity of the two promoters lead to the conclusion that two different DNA loops can form in the ara regulatory region.
Arabinose-induced binding of AraC protein to araI2 activates the araBAD operon promoter.
It is proposed that araI2 occupancy by AraC protein leads to RNA polymerase recognition of the araBAD promoter and that aRAI1 acts as a switch mechanism allowing both the repressor and the activator forms of AraCprotein to regulate the aRABAD promoters.
Mechanism of araC autoregulation and the domains of two overlapping promoters, Pc and PBAD, in the L-arabinose regulatory region of Escherichia coli.
The results suggest that the basis for aRAC autoregulation is that araC protein, in either its activator (P2) or repressor (P1) form, acts as a repressor for aaC, by binding to the RNA polymerase attachment site at the araBAD promoter.
Three binding sites for AraC protein are required for autoregulation of araC in Escherichia coli.
  • E. Hamilton, N. Lee
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1988
It is suggested that AraC exerts its multiplicity of controls through two alternative states of cooperative interactions with DNA and this model presents the interpretations of activation and repression of the araBAD operon and the autoregulation of theAraC gene.
The DNA loop model for ara repression: AraC protein occupies the proposed loop sites in vivo and repression-negative mutations lie in these same sites.
The mutational analysis presented here shows that the DNA components required for repression of araBAD are araI, araO2, and perhaps the aRABAD operon RNA polymerase binding site.
The Escherichia coli L-arabinose operon: binding sites of the regulatory proteins and a mechanism of positive and negative regulation.
The locations of DNA binding by the proteins involved with positive and negative regulation of transcription initiation of the L-arabinose operon in Escherichia coli have been determined and suggest the following regulatory mechanism: induction of the araBAD operon occurs when cyclic AMP receptor protein, araC protein, and RNA polymerase are all present and able to bind to DNA.
Repression and catabolite gene activation in the araBAD operon
Data is presented showing that deletions generated by in vitro mutagenesis of the CAP site led to a five- to sixfold reduction in single-copy araBAD promoter activity in vivo.
An operator at -280 base pairs that is required for repression of araBAD operon promoter: addition of DNA helical turns between the operator and promoter cyclically hinders repression.
A site has been found that is required for repression of the Escherichia coli araBAD operon at -280 and in vitro protection studies showed that araC protein can specifically bind in this area to nucleotides lying at position -265 to -294 with respect to the araBsad operon promoter (PBAD) transcription start point.