Format

Send to:

Choose Destination
See comment in PubMed Commons below
Proc Natl Acad Sci U S A. 2008 Jan 29;105(4):1152-7. doi: 10.1073/pnas.0706067105. Epub 2008 Jan 23.

Regulation of Escherichia coli SOS mutagenesis by dimeric intrinsically disordered umuD gene products.

Author information

  • 1Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Abstract

Products of the umuD gene in Escherichia coli play key roles in coordinating the switch from accurate DNA repair to mutagenic translesion DNA synthesis (TLS) during the SOS response to DNA damage. Homodimeric UmuD(2) is up-regulated 10-fold immediately after damage, after which slow autocleavage removes the N-terminal 24 amino acids of each UmuD. The remaining fragment, UmuD'(2), is required for mutagenic TLS. The small proteins UmuD(2) and UmuD'(2) make a large number of specific protein-protein contacts, including three of the five known E. coli DNA polymerases, parts of the replication machinery, and RecA recombinase. We show that, despite forming stable homodimers, UmuD(2) and UmuD'(2) have circular dichroism (CD) spectra with almost no alpha-helix or beta-sheet signal at physiological concentrations in vitro. High protein concentrations, osmolytic crowding agents, and specific interactions with a partner protein can produce CD spectra that resemble the expected beta-sheet signature. A lack of secondary structure in vitro is characteristic of intrinsically disordered proteins (IDPs), many of which act as regulators. A stable homodimer that lacks significant secondary structure is unusual but not unprecedented. Furthermore, previous single-cysteine cross-linking studies of UmuD(2) and UmuD'(2) show that they have a nonrandom structure at physiologically relevant concentrations in vitro. Our results offer insights into structural characteristics of relatively poorly understood IDPs and provide a model for how the umuD gene products can regulate diverse aspects of the bacterial SOS response.

PMID:
18216271
[PubMed - indexed for MEDLINE]
PMCID:
PMC2234107
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk