RNA Pol III transcriptomes and relationships to Pol II promoters, enhancer-binding factors and chromatin domains

RNA polymerase III transcribes many noncoding RNAs (e.g. tRNAs) important for translational capacity and other functions. Here, we localized RNA polymerase III, alternative TFIIIB complexes (BRF1/2) and TFIIIC in HeLa cells, determining the Pol III transcriptome, defining gene classes, and revealing ‘TFIIIC-only’ sites. Pol III localization in other transformed and primary cell lines revealed both novel and cell-type specific Pol III loci, and one occupied miRNA. Surprisingly, only a fraction of the in silico-predicted Pol III loci are occupied. Interestingly, many occupied Pol III genes reside within an annotated Pol II promoter. Outside of Pol II promoters, occupied Pol III genes overlap with enhancer-like chromatin and enhancer binding proteins such as ETS1 and STAT1. Remarkably, Pol III occupancy scales with the levels of nearby Pol II, active chromatin and CpG content. Taken together, active promoter and enhancer-like chromatin appears to gate Pol III accessibility to the genome. Use of ChIP-array to identify genomic regions bound by RNA Polymerase III machinery