Abstract
DNA replication machinery in plant organelles remains to be characterized. We have biochemically analyzed the DNA synthesis activities of organelle-nuclei isolated from BY-2 cultured tobacco cells and shown that (1) DNA synthesis in both organelles is transiently activated within 24hr after transfer of the cells to fresh medium, (2) plastid- and mitochondrial DNA polymerases are biochemically similar to each other and (3) are more similar to bacterial DNA polymerase I (polI) than to mitochondrial DNA polymeraseγ (polγ) from animals and fungi. Recently, a gene for plastid DNA polymerase was isolated from rice and shown to be homologous to polI. We found, in the tobacco BY-2 EST data bank, an EST clone which corresponds to 3'-5'exonuclease domain of polI. Full-length cDNA sequence encoded polI-like protein potentially targeted to plastids. Phylogenetic analysis showed that the putative tobacco plastid DNA polymerase was more similar to polI than to polγ.
