A gamma-like DNA polymerase in spinach chloroplasts.

A DNA polymerase has been extracted from spinach chloroplasts and purified by chromatography on DEAE-cellulose and hydroxyapatite. A great 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 . poly(rA), optimal requirement for Mn2+ (0.1-1.0 mM), KCl (100 mM) and pH (8-9), high relative molecular mass (approximately 105,000), resistance to aphidicolin and inhibition by N-ethylmaleimide. Some peculiar features of the chloroplast DNA polymerase have, however, been noticed. The mammalian DNA polymerase gamma has been suggested to be responsible for the replication of mitochondrial DNA. Thus, 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 an presence of displacement loops) lead to the suggestion that chloroplast DNA is also replicated by a gamma-like DNA polymerase and that the gamma polymerases present in eukaryotes are, therefore, involved in a strand-displacement DNA synthesis. An alpha-like DNA polymerase activity, present and predominant in crude leaf extracts, was practically absent from purified chloroplast preparations.