The dnaK protein of Escherichia coli possesses an ATPase and autophosphorylating activity and is essential in an in vitro DNA replication system.

The Escherichia coli dnaK gene product, originally defined by mutations that blocked lambda phage DNA replication, is known to be necessary for E. coli viability. We have purified dnaK protein to homogeneity and have demonstrated that it possesses a weak DNA-independent ATPase activity, which results in the production of ADP and Pi. The proof that this ATPase activity is encoded by the dnaK+ gene relies primarily on the fact that the dnaK756 mutation results in the production of an ATPase activity with altered physical properties. The dnaK protein is phosphorylated in vitro and in vivo, probably as a result of an autophosphorylation reaction. The lambda O and P replication proteins were shown to interact in vitro with the dnaK protein. The ATPase activity of the dnaK protein was inhibited by purified lambda P protein and stimulated by purified lambda O protein. Moreover, the dnaK protein participates in the initiation of DNA synthesis in an in vitro DNA replication system that is dependent on the O and P proteins. Anti-dnaK protein immunoglobulin specifically inhibited DNA synthesis in this system.