Identification of the DNA-binding protein, HrcA, of Streptococcus thermophilus

HrcA is a negative transcriptional factor controlling the expression of the stress-specific operons dnaK and groESL in several bacteria. Although the HrcA structural gene has been identified in various organisms, studies at the protein level have been so far limited and mostly restricted to Bacillus subtilis. We have identified the HrcA protein of Streptococcus thermophilus and show here that it is a dimer with a native molecular mass of 74.5 kDa and a sequence-specific DNA-binding activity. Partially denatured and inactive S. thermophilus HrcA recovered its binding activity in the presence of the GroEL chaperone.