A prepriming DNA replication enzyme of Escherichia coli. I. Purification of protein n': a sequence-specific, DNA-dependent ATPase.

Protein n', an enzyme essential for in vitro conversion of single-stranded phiX174 DNA to the duplex replicative form, has been purified about 16,000-fold from Escherichia coli. The enzyme is a single polypeptide chain with a native molecular weight of 76,000; about 70 enzyme molecules are present in an E. coli cell. Nearly homogeneous preparations display an ATPase (dATPase) activity which depends on a unique sequence in the phiX174 DNA. Replicative activity of n' protein and its phiX174 DNA-dependent ATPase activity were present in a constant ratio during the latter stages of purification, upon sedimentation in a glycerol gradient, and during heat inactivation. Further studies of the properties of protein n' are presented in a succeeding paper.