TFIIIC regulates SMC complex binding and 3D DNA contacts between tRNA genes

Transcription factor IIIC (TFIIIC) is a multi-subunit protein complex that recruits RNA polymerase III (Pol III) to the majority of its target genes. Evolutionarily conserved overlap between TFIIIC binding sites and the structural maintenance of chromosomes (SMC) complexes suggested a role for TFIIIC in SMC regulation and 3D organization of eukaryotic genomes; but the evidence has remained largely correlational due to the essential role of TFIIIC in recruiting RNA Pol III for transcription initiation. Here, we directly tested the function of TFIIIC in SMC complex regulation by using auxin inducible protein degradation in C. elegans. We performed Hi-C and ChIP-seq analyses upon acute depletion of TFTC-3, an essential TFIIIC subunit, and RPC-1, the catalytic subunit of RNA Pol III. Our results showed that TFIIIC is required for the binding of cohesin and condensin complexes to tRNA genes. TFIIIC is also required for increasing 3D contacts between distant tRNA genes located on the same or different chromosomes. Depletion of individual SMC complexes did not significantly reduce the tRNA gene contacts, suggesting redundancy or an independent mechanism of interphase genome organization mediating the 3D contacts between tRNA genes. Together, our study supports an RNA Pol III independent function for TFIIIC in regulating multiple SMC complexes and the 3D organization of tRNA genes.