Purification and properties of a pea chloroplast DNA polymerase

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Abstract
A DNA polymerase was purified > 3000-fold from the chloroplasts of pea plants by chromatography on DEAE-cellulose, phosphocellulose, single-stranded DNA-agarose and sedimentation in a glycerol gradient. Electrophoretic analysis on polyacrylamide gels in the presence of sodium dodecyl sulfate indicates that the final fraction contained a single discernible protein band of 90,000 daltons. Gel filtration on Sephacryl S-200 and glycerol gradient sedimentation under nondenaturing conditions demonstrate that the chloroplast DNA polymerase has a native molecular mass of approximately 87,000 daltons. The purified polymerase lacks any associated nuclease activity. The enzyme activity is inhibited by N-ethylmaleimide (74% at 1.0 mM) and ethidium bromide (90% at 0.23 mM) and is resistant to aphidicolin. The purified enzyme is totally dependent on the presence of added DNA, has an absolute requirement for Mg2+ (12 mM optimal) is stimulated by K+ (120 mM optimal), and requires all 4 deoxynucleoside triphosphates for maximum activity. Native DNA which has been degraded to a limited extent with DNase I is the most efficient template.