What is RNA polymerase III?

In eukaryote cells, RNA polymerase III is a protein that transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs.

The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions. Therefore, the regulation of Pol III transcription is primarily tied to the regulation of cell growth and the cell cycle, thus requiring fewer regulatory proteins than RNA polymerase II. Under stress conditions however, the protein Maf1 represses Pol III activity. Rapamycin is another Pol III inhibitor via its direct target TOR.