General Function
RNA polymerase III is part of the transcription machinery of eukaryotes. It handles genes encoding for small structured RNAs: tRNA, spliceosomal U6 snRNA and 5S rRNA. RNA polymerase III is the largest eukaryotic RNA polymerase, yet it is the least characterized.
Elongation is the process of adding nucleotides to a growing RNA strand. Together, the polymerase, the template DNA, and the growing mRNA strand form the elongation complex. RNA polymerase III is composed of mobile elements which move relative to each other; conformational changes result throughout the transcription process as a result of this movement.
This page contains information about subunits of RNA polymerase III which are relevant to transcription in the polymerase's elongation complex.
Specific Interactions
The of the polymerase moves the DNA, allowing transcription to proceed. It functions in translocation of pol III, moving the polymerase down the template DNA strand, so that nucleotides may be added continuously. RPC1 is the largest subunit of pol III.
RPC2 contributes to catalytic activity in the polymerase, and forms the active center of the polymerase along with RPC1. It is suggested that RPC2 helps to open and close the cleft where transcription takes place. The two subunits RPC1 and RPC2 form a bridging helix that crosses the cleft near the active site and binds to the nascent RNA transcript. This helix acts as a ratchet that moves the enlongating transcript through RNA pol III.
RPC6 recruits pol III to the preinitiation complex, and contributes to an initiation-competent configuration for RNA pol III.
RPC10 is involved in transcription reinitiation and RNA cleavage during termination.
The RPC25/RPC8-RPC17/RPC9 subcomplex binds the transcripts emerging from the exit pore, which facilitates elongation.
The RPC53/RPC4-RPC37/RPC5 subcomplex functions to terminate transcription and reinitiate transcription, by providing a binding site for the terminator.
Origin
RNA Polymerase III is used by all eukaryotes in transcription of DNA to mRNA. This process takes place in the nucleus of the cell. The structure shown on this page was elucidated by electron cryomicroscopy of Saccharomyces cerevisiae (bakers yeast). The structure was taken from a 2015 deposition to PDB by Hoffman et al.
