Structure of the multi-subunit chloroplast RNA polymerase

Mol Cell. 2024 Mar 7;84(5):910-925.e5. doi: 10.1016/j.molcel.2024.02.003. Epub 2024 Feb 29.


Chloroplasts contain a dedicated genome that encodes subunits of the photosynthesis machinery. Transcription of photosynthesis genes is predominantly carried out by a plastid-encoded RNA polymerase (PEP), a nearly 1 MDa complex composed of core subunits with homology to eubacterial RNA polymerases (RNAPs) and at least 12 additional chloroplast-specific PEP-associated proteins (PAPs). However, the architecture of this complex and the functions of the PAPs remain unknown. Here, we report the cryo-EM structure of a 19-subunit PEP complex from Sinapis alba (white mustard). The structure reveals that the PEP core resembles prokaryotic and nuclear RNAPs but contains chloroplast-specific features that mediate interactions with the PAPs. The PAPs are unrelated to known transcription factors and arrange around the core in a unique fashion. Their structures suggest potential functions during transcription in the chemical environment of chloroplasts. These results reveal structural insights into chloroplast transcription and provide a framework for understanding photosynthesis gene expression.

Keywords: RNA; RNA polymerase; chloroplast; cryo-EM; gene expression; organelle; photosynthesis; plastid; structural biology; transcription.

MeSH terms

  • Chloroplasts / genetics
  • Chloroplasts / metabolism
  • DNA-Directed RNA Polymerases* / genetics
  • DNA-Directed RNA Polymerases* / metabolism
  • Gene Expression Regulation, Plant
  • Plastids / genetics
  • Plastids / metabolism
  • RNA, Chloroplast* / metabolism
  • Transcription, Genetic


  • RNA, Chloroplast
  • DNA-Directed RNA Polymerases