Subunit structures of Arabidopsis RNA Polymerase IV complexes
EMSL Project ID
24795
Abstract
All eukaryotes have three conventional nuclear DNA-dependent RNA polymerases, abbreviated as Pol I, Pol II and Pol III. Pol I transcribe 45S pre-rRNA, pol II transcribes mRNAs and pol III transcribes small (<400 nt) structural RNAs that include 5S rRNA and tRNAsy. Remarkably, plants have evolved an additional fourth class of nuclear RNA polymerase that is required for the production and functioning of nuclear small interfering RNAs (siRNAs). These nuclear siRNAs mediate RNA-directed DNA methylation and the silencing of repetitive sequences throughout the genome. In Arabidopsis thaliana, there are two alternative Pol IV largest subunits that are encoded by different genes, NRPD1a or NRPD1b. These largest subunits each interact with a second-largest subunit, NRPD2 encoded by a single gene, thereby defining two alternative forms of Pol IV, namely Pol IVa or Pol IVb. The two forms of Pol IV have non-redundant functions, with Pol IVa being required for the production of siRNAs and pol IVb acting later in the RNA-directed DNA methylation pathway. Pol IVa and Pol IVb appear to lack conventional DNA-dependent RNA polymerase activity and their templates and enzymatic products are unknown. Preliminary data suggest that Pol IVa and Pol IVb are multi-subunit complexes that might utilize some of the same 12-17 subunits found in RNA polymerases I, II or III. We seek the collaboration of EMSL scientists to identify the subunits of Pol IVa and Pol IVb using state-of-the-art mass spectrometry techniques in order to gain insight into the structures and functions of these enigmatic activities.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-05-25
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members