A combinatorial approach to uncover a novel Integrator subunit

RNA polymerase II (RNAPII) controls the expression of all protein coding genes and most noncoding loci in higher eukaryotes. The ultimate rate of transcription is regulated at the level of multiple checkpoints during the transcription cycle (initiation, pausing, termination). Calibrating the activity of RNAPII is fundamental to all cellular processes and requires an assortment of polymerase-associated factors that are recruited at sites of active transcription. The Integrator complex is one of the most elusive transcriptional regulators in metazoans, deemed to be recruited after initiation to help establish and modulate paused RNAPII. Recent structural, biochemical, and functional evidence suggest that Integrator is composed of 14 subunits that assemble and operate in a modular fashion. We employed proteomics and machine-learning structure prediction (AlphaFold2) approaches to identify a novel Integrator subunit, INTS15. We report that INTS15 assembles primarily with the INTS13/INTS14/INTS10 module and interfaces with the core of the Int-PP2A complex. Functional genomics analysis further reveals a role for INTS15 in modulating RNAPII pausing at a subset of genes in human cell lines. Our study shows that omics approaches combined with AlphaFold2-based predictions provide novel insights into the molecular architecture of large and flexible multiprotein complexes.