Display Settings:

Format

Send to:

Choose Destination
See comment in PubMed Commons below
Mol Microbiol. 2008 Apr;68(2):448-61. doi: 10.1111/j.1365-2958.2008.06164.x.

Differences in the mechanism of the allosteric l-rhamnose responses of the AraC/XylS family transcription activators RhaS and RhaR.

Author information

  • 1Department of Molecular Biosciences, University of Kansas, Lawrence, KS, USA.

Abstract

Proteins in the largest subset of AraC/XylS family transcription activators, including RhaS and RhaR, have C-terminal domains (CTDs) that mediate DNA-binding and transcription activation, and N-terminal domains (NTDs) that mediate dimerization and effector binding. The mechanism of the allosteric effector response in this family has been identified only for AraC. Here, we investigated the mechanism by which RhaS and RhaR respond to their effector, l-rhamnose. Unlike AraC, N-terminal truncations suggested that RhaS and RhaR do not use an N-terminal arm to inhibit activity in the absence of effector. We used random mutagenesis to isolate RhaS and RhaR variants with enhanced activation in the absence of l-rhamnose. NTD substitutions largely clustered around the predicted l-rhamnose-binding pockets, suggesting that they mimic the structural outcome of effector binding to the wild-type proteins. RhaS-CTD substitutions clustered in the first HTH motif, and suggested that l-rhamnose induces improved DNA binding. In contrast, RhaR-CTD substitutions clustered at a single residue in the second HTH motif, at a position consistent with improved RNAP contacts. We propose separate allosteric mechanisms for the two proteins: Without l-rhamnose, RhaS does not effectively bind DNA while RhaR does not effectively contact RNAP. Upon l-rhamnose binding, both proteins undergo structural changes that enable transcription activation.

PMID:
18366439
[PubMed - indexed for MEDLINE]
PMCID:
PMC2377013
Free PMC Article

Images from this publication.See all images (6)Free text

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6

Publication Types, MeSH Terms, Substances, Grant Support

PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Blackwell Publishing Icon for PubMed Central
    Loading ...
    Write to the Help Desk