Function of DnaJ and DnaK as chaperones in origin-specific DNA binding by RepA

HEAT-shock proteins are normal constituents of cells whose synthesis is increased on exposure to various forms of stress. They are interesting because of their ubiquity and high conservation during evolution. Two families of heat-shock proteins, hsp60s and hspTOs, have been implicated in accelerating protein folding and oligomerization and also in maintaining proteins in an unfolded state, thus facilitating membrane transport1–5. The Escherichia coli hspTO analogue, DnaK, and two other heat-shock proteins, DnaJ and GrpE, are required for cell viability at high temperatures and are involved in DNA replication of phage λ and plasmids P1 and F6–10. These three proteins are involved in replication in vitro of PI DNA along with many host replication proteins and the PI RepA initiator protein11,12. RepA exists in a stable protein complex with DnaJ containing a dimer each of RepA and DnaJ11. We report here that DnaK and DnaJ mediate an alteration in the PI initiator protein, rendering it much more active for oriP1 DNA binding.