A γ‐like DNA Polymerase in Spinach Chloroplasts

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Abstract
A DNA polymerase was extracted from spinach chloroplasts and purified by chromatography on DEAE-cellulose and hydroxyapatite. Similarity between the purified chloroplast polymerase and the mammalian mitochondrial DNA polymerase .gamma. was found by several criteria: preference for the synthetic primer-template (dT)12-18 .cntdot. poly(rA), optimal requirement for Mn2+ (0.1-1.0 mM), KCl (100 mM) and pH (8-9), high relative MW (.apprx. 105,000), resistance to aphidicolin and inhibition by N-ethylmaleimide. Some peculiar features of the chloroplast DNA polymerase were noticed. The mammalian DNA polymerase .gamma. may be responsible for the replication of mitochondrial DNA. Both the presence of a .gamma.-like DNA polymerase in chloroplasts and the similarities between the chloroplast and the mitochondrial DNA (absence of a nucleosomal structure and presence of displacement loops) suggest that chloroplast DNA was replicated by a .gamma.-like DNA polymerase and .gamma.-polymerases present in eukaryotes may be involved in a strand-displacement DNA synthesis. An .alpha.-like DNA polymerase activity, present and predominant in crude leaf extracts, was absent from purified chloroplast preparations.