Abstract
Plastids are descended from a cyanobacterial symbiosis and have bacterial type RNA polymerase (PEP). However, recent plastids proteome analyses revealed that higher plant plastids contain not only prokaryotic proteins derived from the ancestor, but also several eukaryotic proteins acquired from host cells during plant evolution. We focused on a component of chloroplast transcriptional active chromosome: pTAC3, which has a eukaryotic-type DNA binding domain (sap domain). The pTAC3 knock-out mutants showed albino phenotype and expression of PEP-dependent genes was significantly suppressed in the mutants. To determine the binding sites for pTAC3 in Arabidopsis chloroplast genome, we performed a chloroplast ChIP assay. pTAC3 binds mainly to transcription units that are transcribed by PEP such as psbA. Gel shift analysis revealed that a GST-tagged sap domain fragment has DNA binding activity, while the sequence specificity is weak. These results suggest that pTAC3 might function as a regulatory factor of PEP.
