Abstract
We have isolated two genes encoding bacterial DNA polymerase I homologues from BY-2 cultured tobacco cells, and named them NtpolI-like 1 and NtpolI-like 2. The two genes were highly similar to each other (97.2% identical at amino acid sequence level), suggesting that they were orthologous genes each derived from respective progenitor species of Nicotiana tabacum, an allotetraploid plant. Although plastid localization was predicted for the both gene products, western blotting analyses, as well as experiments with NtpolI-like1/2-GFP fusion proteins, demonstrated dual-targeting of the gene products to plastids and mitochondria, suggesting that the DNA replication in the plastids and mitochondria might be conducted by the same DNA polymerase. Further biochemical analyses to examine the relationships between (i) NtpolI-like1/2 gene products and organelle DNA polymerases and (ii) DNA polymerases present in the plastids and mitochondria are now on progress, using plastid- and mitochondrial nuclei isolated from BY-2 cultured tobacco cells.
