Three-dimensional envelope and subunit interactions of the plastid-encoded RNA polymerase from Sinapis alba

Abstract

RNA polymerases (RNAPs) involved in gene transcription are found in all living organisms with degrees of complexity ranging from single polypeptide chains to multimeric enzymes. In the chloroplasts, the nuclear-encoded RNA polymerase and the plastid-encoded RNA polymerase (PEP) are both involved in the selective transcription of the plastid genome. The PEP is a prokaryotic-type multimeric RNAP found in different states depending on light stimuli and cell identity. One of its active states requires the assembly of nuclear-encoded PEP-Associated Proteins (PAPs) on the catalytic core, producing a complex of more than 900 kDa regarded as essential for chloroplast biogenesis. A purification procedure compatible with structural analysis was used to enrich the native PEP from Sinapis alba chloroplasts.