Abstract
The micro-environment in the chloroplast is drastically changed in the day/night cycle. Since PS reaction center proteins such as D1 protein are rapidly turned over, gene expression must be regulated through sensing the environmental change. Transcription of these genes is accomplished with an eubacterial-type RNA polymerase (PEP), which requires sigma factors. We have made Arabidopsis transgenic with wild-type and putative phosphorylation sites-deleted SIG1 molecules, the major species of sigma factors. We performed run-on transcription with isolated chloroplasts from the transgenic lines. The plants were also labeled with [32P]orthophosphate in vivo and SIG1 was recovered with antibodies. Molecular mass of complexes associated with SIG1 was examined by sucrose density gradient centrifugation. The overall results lead to the conclusion that the phosphorylation of SIG1 with Ser/Thr protein kinase in the dark interferes with formation of active holoenzyme to transcribe the photosynthesis genes.
