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The nucleoid-associated protein StpA binds curved DNA, has a greater DNA-binding affinity than H-NS and is present in significant levels in hns mutants
February 2001
February 2001
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Abstract
The StpA protein is closely related to H-NS, the well-characterised global regulator
of gene expression which is a major component of eubacterial chromatin. Despite sharing
a very high degree of sequence identify and having biochemical properties in common
with H-NS, the physiological function of StpA remains unknown. We show that StpA exhibits
similar DNA-binding activities to H-NS. Although both display a strong preference
for binding to curved DNA, StpA binds DNA with a four-fold higher affinity than H-NS,
with K(d)s of 0.7 microM and 2.8 microM, respectively. It has previously been reported
that expression of stpA is derepressed in an hns mutant. We have quantified the amount
of StpA protein produced under this condition and find it to be only one-tenth the
level of H-NS protein in wild-type cells. Our findings explain why the presence of
StpA does not compensate for the lack of H-NS in an hns mutant, and why the characteristic
pleiotropic hns mutant phenotype is observed.