Pol III promoters. Pol III promoters are found within genes. (a) The Pol III tRNA promoter uses the Box A and Box B sequence elements and is bound by transcription factors TFIIIB and TFIIIC. (b) The Pol III 5S rRNA promoter uses Box A and Box C, as well as TFIIIB, TFIIIC, and TFIIIA. Together, these factors recruit Pol III to the transcription start site.