DNA synthesis in isolated chloroplasts and chloroplast extracts of maize

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Abstract
Isolated chloroplasts are capable of synthesizing chloroplast DNA in the presence of Mg2+ and deoxynucleoside triphosphates. The in vitro reaction proceeds for at least 60 min and is inhibited by KCl and N-ethylmaleimide. Stretches of several hundred nucleotides in length are synthesized within an hour. Little or no inhibition is shown by aphidicolin (an inhibitor of eukaryotic DNA polymerase .alpha.), dideoxythymidien triphosphate (an inhibitor of eukaryotic DNA polymerases .beta. and .gamma.), nalidixic acid or rifampicin. Ethidium bromide is a moderate inhibitor of DNA synthesis in the isolated chloroplast. Soluble extracts of chloroplasts will copy exogenously added recombinant plasmid circular DNA containing fragments of chloroplast DNA, and this reaction is strongly inhibited by ethidium bromide. Copying of the plasmid DNA [plasmid pZmc100] takes place on the relaxed circular or linear forms of the DNA, but no specific initiation sites on the chloroplasts'' DNA fragments of the recombinant plasmids were detected. The data are consistent with a repair mechanism operating in vitro but may also represent incomplete replicative DNA synthesis.

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