<p> The <taxon tax_id="562">Escherichia coli</taxon> Hsp40 DnaJ and Hsp70 DnaK cooperate in the binding of proteins at intermediate stages of folding, assembly, and translocation across membranes [<cite idref="PUB00010645"/>]. Binding of protein substrates to the DnaK C-terminal domain is controlled by ATP binding and hydrolysis in the N-terminal ATPase domain. The interaction of DnaJ with DnaK is mediated at least in part by the highly conserved N-terminal J-domain of DnaJ. The J-domain interaction is localized to the ATPase domain of DnaK and is likely to be dominated by electrostatic interactions. J-domain may tether DnaK to DnaJ-bound substrates, which DnaK then binds with its C-terminal peptide-binding domain. The peptide-binding domain of DnaJ is comprised of a beta sandwich made up of 6 beta-strands divided into 2 sheets.</p>