Interaction of RecA protein with acidic phospholipids inhibits DNA-binding activity of RecA

The RecA protein of Escherichia coli binds specifically to acidic phospholipids such as cardiolipin and phosphatidylglycerol. This binding appears to be affected by the presence of divalent cations such as Ca2+ and Mg2+. The interaction leads to the inhibition of RecA binding to at least two different conformations of DNA, single-stranded DNA and left-handed Z-DNA, thus suggesting that the phospholipids interact at the DNA-binding site of the RecA protein. Inclusion of a nucleotide cofactor [adenosine 5'-O-(gamma-thiotriphosphate)] in the reactions did not prevent the inhibition of DNA-binding activities of RecA protein by the phospholipids. The interaction of RecA protein with cardiolipin and phosphatidylglycerol, which represent two of the three major phospholipids of the E. coli membrane, may be physiologically important, as it provides a possible mechanism for the RecA-membrane association during the SOS response. These observations raise the possibility that the Z-DNA-binding activity of RecA protein is merely a manifestation of its phospholipid-binding property.