PagR is a transcriptional repressor in Bacillus anthracis that controls the
chromosomal S-layer genes eag and sap, and downregulates the protective antigen
pagA gene by direct binding to their promoter regions. The PagR protein sequence
is similar to those of members of the ArsR repressor family involved in the
repression of arsenate-resistance genes in numerous bacteria. The crystal
structure of PagR was solved using multi-wavelength anomalous diffraction (MAD)
techniques and was refined with 1.8 A resolution diffraction data. The PagR
molecules form dimers, as observed in all SmtB/ArsR repressor family proteins.
In the crystal lattice four PagR dimers pack together to form an inactive
octamer. Model-building studies suggest that the dimer binds to a DNA duplex
with a bend of around 4 degrees.