Subunit compositions of Arabidopsis RNA polymerases I and III reveal Pol I- and Pol III-specific forms of the AC40 subunit and alternative forms of the C53 subunit

Nucleic Acids Res. 2015 Apr 30;43(8):4163-78. doi: 10.1093/nar/gkv247. Epub 2015 Mar 26.


Using affinity purification and mass spectrometry, we identified the subunits of Arabidopsis thaliana multisubunit RNA polymerases I and III (abbreviated as Pol I and Pol III), the first analysis of their physical compositions in plants. In all eukaryotes examined to date, AC40 and AC19 subunits are common to Pol I (a.k.a. Pol A) and Pol III (a.k.a. Pol C) and are encoded by single genes. Surprisingly, A. thaliana and related species express two distinct AC40 paralogs, one of which assembles into Pol I and the other of which assembles into Pol III. Changes at eight amino acid positions correlate with the functional divergence of Pol I- and Pol III-specific AC40 paralogs. Two genes encode homologs of the yeast C53 subunit and either protein can assemble into Pol III. By contrast, only one of two potential C17 variants, and one of two potential C31 variants were detected in Pol III. We introduce a new nomenclature system for plant Pol I and Pol III subunits in which the 12 subunits that are structurally and functionally homologous among Pols I through V are assigned equivalent numbers.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / immunology
  • Arabidopsis Proteins / isolation & purification
  • Protein Subunits / chemistry*
  • Protein Subunits / genetics
  • Protein Subunits / immunology
  • Protein Subunits / isolation & purification
  • RNA Polymerase I / chemistry*
  • RNA Polymerase I / genetics
  • RNA Polymerase I / immunology
  • RNA Polymerase I / isolation & purification
  • RNA Polymerase III / chemistry*
  • RNA Polymerase III / genetics
  • RNA Polymerase III / immunology
  • RNA Polymerase III / isolation & purification
  • Terminology as Topic


  • Arabidopsis Proteins
  • Protein Subunits
  • RNA Polymerase I
  • RNA Polymerase III