Obaji, D. | bioRxiv Science

bioRxiv2026

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.

genomics↗

bioRxiv2021

Topoisomerases I and II facilitate condensin DC translocation to organize and repress X chromosomes in C. elegans

Condensin complexes are evolutionarily conserved molecular motors that translocate along DNA and form loops. While condensin-mediated DNA looping is thought to direct the chain-passing activity of topoisomerase II to separate sister chromatids, it is not known if topological constraints in turn regulate loop formation in vivo. Here we applied auxin inducible degradation of topoisomerases I and II to determine how DNA topology affects the translocation of an X chromosome specific condensin that represses transcription for dosage compensation in C. elegans (condensin DC). We found that both topoisomerases colocalize with condensin DC and control its movement at different genomic scales. TOP-2 depletion hindered condensin DC translocation over long distances, resulting in accumulation around its X-specific recruitment sites and shorter Hi-C interactions. In contrast, TOP-1 depletion did not affect long-range spreading but resulted in accumulation of condensin DC within expressed gene bodies. Both TOP-1 and TOP-2 depletions resulted in X chromosome transcriptional upregulation indicating that condensin DC translocation at both scales is required for its function in gene repression. Together the distinct effects of TOP-1 and TOP-2 on condensin DC distribution revealed two distinct modes of condensin DC association with chromatin: long-range translocation that requires decatenation/unknotting of DNA and short-range translocation across genes that requires resolution of transcription-induced supercoiling.

molecular biology↗