Send to

Choose Destination
See comment in PubMed Commons below
J Biol Chem. 1995 Sep 8;270(36):20908-14.

Binuclear [2Fe-2S] clusters in the Escherichia coli SoxR protein and role of the metal centers in transcription.

Author information

  • 1Department of Molecular and Cellular Toxicology, Harvard University, School of Public Health, Boston, Massachusetts 02115, USA.


SoxR protein of Escherichia coli is activated by superoxide-generating agents or nitric oxide as a powerful transcription activator of the soxS gene, whose product activates approximately 10 other promoters. SoxR contains non-heme iron essential for abortive initiation of transcription in vitro. Here we show that this metal dependence extends to full-length transcription in vitro. In the presence of E. coli sigma 70 RNA polymerase, iron-containing SoxR mediates open complex formation at the soxS promoter, as determined using footprinting with Cu-5-phenyl-1,10-phenanthroline. We investigated the nature of the SoxR iron center by chemical analyses and electron paramagnetic resonance spectroscopy. Dithionite-reduced Fe-SoxR exhibited an almost axial paramagnetic signature with g values of 2.01 and 1.93 observable up to 100 K. These features, together with quantitation of spin, iron, and S2-, and hydrodynamic evidence that SoxR is a homodimer in solution, indicate that (SoxR)2 contains two [2Fe-2S] clusters. Treatment of Fe-SoxR with high concentrations of dithiothreitol caused subtle changes in the visible absorption spectrum and blocked transcriptional activity without generating reduced [2Fe-2S] centers, but was also associated with the loss of iron from the protein. However, lowering the thiol concentration by dilution allowed spontaneous regeneration of active Fe-SoxR.

[PubMed - indexed for MEDLINE]
Free full text
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire
    Loading ...
    Support Center