DNA binding properties of the hfq gene product of Escherichia coli.

We found that plasmids isolated by alkaline-lysis method occasionally showed abnormal mobility on agarose gel electrophoresis. This abnormality was not detected after phenol extraction of plasmids, indicating that it was caused by proteinous factor(s). A 15-kDa protein was found in the plasmid preparations on SDS-PAGE. The sequence of eighteen N-terminal amino acid residues of the 15-kDa protein was identical with the host factor I (HF-I) encoded by the hfq gene at 95 min on the Escherichia coli chromosome map, which is known to be required for bacteriophage Qbeta replication. The HF-I protein was purified and in vitro DNA binding experiment was carried out. HF-I bound to both supercoiled DNA and linear DNA and the binding of HF-I seemed to be sequence-nonspecific.