Terminator-dependent facilitated recycling of RNA polymerase III couples transcriptional activation and chromatin remodeling in vivo

Termination is a crucial step in generating the functional transcriptome of a cell. The short genes transcribed by RNA polymerase (pol) III are mostly found in the highly transcribed genomic loci. The mechanism responsible for their high transcription rate in vivo is not yet established. Transcription terminator-dependent facilitated recycling of pol III on naked DNA templates is reported to increase transcriptional output in vitro. We found that apart from defining the 3-end of transcript, the transcription terminator is essential for achieving high-level chromatin transcription by pol III in vitro and in vivo. Using terminator-deficient SNR6 gene templates or a recycling deficient pol III mutant, we show that the TFIIIC-dependent transcriptional activation of chromatin is a process with three closely linked components, viz. anti-repression to naked DNA levels with TFIIIC binding, TFIIIC-dependent chromatin remodeling for better accessibility of the sequence elements and terminator-directed full transcriptional activation. Measurement of pol III occupancy on different gene regions demonstrated a direct link between the high transcription rate and the terminator dependent recycling of pol III in vivo. This novel regulatory mechanism may be generally applicable to the highly transcribed genes in any cell and even for cancer management wherein pol III transcription is found highly elevated.