Structural insights into human TFIIIC promoter recognition

Abstract

Transcription factor (TF) IIIC recruits RNA polymerase (Pol) III to most of its target genes. Recognition of intragenic A- and B-box motifs in transfer RNA (tRNA) genes by TFIIIC modules τA and τB is the first critical step for tRNA synthesis but is mechanistically poorly understood. Here, we report cryo–electron microscopy structures of the six-subunit human TFIIIC complex unbound and bound to a tRNA gene. The τB module recognizes the B-box via DNA shape and sequence readout through the assembly of multiple winged-helix domains. TFIIIC220 forms an integral part of both τA and τB connecting the two subcomplexes via a ~550–amino acid residue flexible linker. Our data provide a structural mechanism by which high-affinity B-box recognition anchors TFIIIC to promoter DNA and permits scanning for low-affinity A-boxes and TFIIIB for Pol III activation.

The Conserved Chromatin Remodeler SMARCAD1 Interacts with TFIIIC and Architectural Proteins in Human and Mouse

“…Peptides corresponding to five of the six members of the TFIIIC complex (TFIIIC220,110,102, 90, and 63) were prominent in the interactome from HEK293 cells ( Figure 1 ; Supplementary Figure S1 ) [ 57 ]. Given the dual role of TFIIIC in transcription and chromosome organization [ 13 , 15 , 16 , 22 , 60 ], a partnership with TFIIIC may reflect a role of SMARCAD1 in the regulation of RNA polymerase III transcription or alternatively in chromosome architecture or possibly a contribution to both. We therefore interrogated the published SMARCAD1 interactome from the HEK293 cell for the presence of other proteins with acknowledged roles in either polymerase III transcription or chromatin architecture alongside TFIIIC.…”

“…( b ) The six polypeptides of the hTFIIIC complex and their known interactions according to the STRING physical network. TFIIIC complex division into two sub-complexes is indicated; modules A and B bind A and B box DNA loci, respectively [ 60 ]. Shown in bold are the five subunits that were identified by mass spectrometry as associated with tagged, overexpressed SMARCAD1 by [ 57 ].…”

“…To this end, we performed co-immunoprecipitation experiments in HeLa nuclear extracts with antibodies recognizing the two distinct TFIIIC sub-complexes, which together form a stable functional complex (Figure 2). Structural, biochemical, and genetic approaches have implicated the largest subunits, namely TFIIIC102 and TFIIIC220, in linking the two sub-complexes [60,[67][68][69]. A presentation of known extensive interactions between the individual subunits taken from the STRING database (https://string-db.org accessed on 14 July 2023) is shown in Figure 1b.…”