Crystal structure of ω transcriptional repressor encoded by Streptococcus pyogenes plasmid pSM19035 at 1.5 Å resolution

Kazutaka Murayama, Peter Orth, Ana B. De La Hoz, Juan C. Alonso, Wolfram Saenger

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63 Citations (Scopus)


The 71 amino acid residue ω protein encoded by the Streptococcus pyogenes non-conjugative plasmid pSM19035 is a transcriptional repressor that regulates expression of genes for copy number control and stable maintenance of plasmids. The crystal structure of ω protein has been determined by multiple isomorphous replacement, including anomalous scattering and refined to an R-factor of 21.1% (Rfree = 23.2 %) at 1.5 Å resolution. Two monomers related by a non-crystallographic 2-fold axis form a homodimer that occupies the asymmetric unit. Each polypeptide chain is folded into two α-helices and one β-strand forming an antiparallel β-ribbon in the homodimer. The N-terminal regions (1-23 and 1-22 in subunits I and II, respectively) are not defined in the electron density due to proteolysis of the N-terminal 20 amino acid residues during crystallisation and partial disorder. The ω protein belongs to the structural super-family of MetJ/Arc repressors featuring a ribbon-helix-helix DNA-binding motif with the β-ribbon located in and recognizing the major groove of operator DNA; according to a modelled ω protein-DNA complex, residues Arg31 and Arg31′ on the β-ribbon are in positions to interact with a nucleobase, especially guanine.

Original languageEnglish
Pages (from-to)789-796
Number of pages8
JournalJournal of Molecular Biology
Issue number4
Publication statusPublished - 2001 Dec 7
Externally publishedYes


  • MetJ/Arc superfamily
  • Ribbon-helix-helix motif
  • Transcriptional repressor
  • X-ray crystal structure
  • ω protein

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Molecular Biology


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