A holoenzyme form of deoxyribonucleic acid polymerase III. Isolation and properties.

A new form of DNA polymerase III (pol III), termed holoenzyme, has been purified to apparent homogeneity from gently lysed Escherichia co2i. Three forms of pol III have now been recognized on the bases of their distinctive physical characteristics and their capacity to utilize a predominantly single-stranded template: (a) pol III, a dimer of 90,000-dalton subunits, which is inactive on single-stranded circular DNA (SS DNA) ; (b) pol III*, a higher polymer of pol III, which is active on SS DNA only in the presence of copolymerase III* (cop01 III*), a 77,000-dalton polypeptide; and (c) holoenzyme, a 330,000-dalton tetramer composed of the two pol III subunits and two cop01 III* units, which is distinguished from pol III or pol III* by its activity on SS DNA in the absence of added cop01 III*. The holoenzyme is dissociated into p01 III* and cop01 III* by chromatography on phosphocellulose; pol III* is converted to pol III by heating, dilution, or aging. Like pol III*, the holoenzyme requires ATP to form an initiation complex with the primer template.