DNA polymerase III holoenzyme of Escherichia coli. I. Purification and distinctive functions of subunits tau and gamma, the dnaZX gene products.

摘要: Escherichia coli dnaZX, the gene which when mutant blocks DNA chain elongation, was cloned into a lambda PL promoter-mediated expression vector. In cells carrying this plasmid, activity that complements dnaZ extract in replicating primed single-stranded circle increased about 20-fold. Two polypeptides of 71 and 52 kDa were overproduced. Upon fractionation, two complementing activities purified to homogeneity proved be 71- 52-kDa polypeptides. Immunoassays revealed their respective identities with tau gamma subunits polymerase III holoenzyme. The N-terminal amino acid sequences first 12 residues identical both subunits, as molar specific complementation. Thus, subunit defect holoenzyme from dnaZts strain efficiently does subunit. Inasmuch 71-kDa (tau) can also overcome enzymatic dnaX strain, polypeptide has dual replication functions, only one performed by Availability pure for study provided basis proposing an asymmetry structure function dimeric