Abstract
Chloroplasts retain bacterial type RNA polymerase, PEP; plastid encoded plastid RNA polymerase that originated from ancestral cyanobacterium endosymbiont and transcribes photosynthesis genes, while prokaryotic genes encoding RNA polymerase (RNAP) accessory proteins have been lost in plant genome. Interestingly, chloroplast proteomic data suggest that PEP forms a large RNAP complex with eukaryotic type DNA binding proteins. However, the molecular function of the PEP associated eukaryotic proteins in chloroplast transcription remains unknown. pTAC3 is a PEP associated eukaryotic DNA binding protein that is conserved only in land plants. We examined the association of PEP and pTAC3 with chloroplast DNA by using chromatin immunoprecipitation assay, ChIP. ChIP assay in wheat chloroplasts using RpoA specific antibody showed that PEP is associated with transcription unit of PEP. Interestingly, pTAC3 showed the similar association pattern with the PEP transcription units. These data suggest that pTAC3 is associated with not only transcription initiation complex but also elongation complex of PEP in vivo.
