The Integrator complex controls the termination of transcription at diverse classes of gene targets

Complexes containing INTS3 and either NABP1 or NABP2 were initially characterized in DNA damage responses, but their biochemical function remained unknown. Using affinity purifications and HIV Integration Targeting-Sequencing (HIT-Seq), we find that these complexes are part of the Integrator complex, which binds RNA Polymerase II and regulates specific target genes. Integrator cleaves snRNAs as part of their processing to their mature form in a mechanism that is intimately coupled with transcription termination. However, HIT-Seq reveals that Integrator also binds to the 3’ end of replication-dependent histones and promoter proximal regions of genes with polyadenylated transcripts. Depletion of Integrator subunits results in transcription termination failure, disrupting histone mRNA processing, and leading to polyadenylation of snRNAs and histone mRNAs. Furthermore, promoter proximal binding of Integrator negatively regulates expression of genes whose transcripts are normally polyadenylated. Integrator recruitment to all three gene classes is DSIF-dependent, suggesting that Integrator functions as a termination complex at DSIF-dependent RNA Polymerase II pause sites. HITseq was used to interrogate chromatin binding sites of of proteins in the complex (including INIP, INTS3, INTS9, INTS11, NABP1, NABP2, NELFA, NELFB, NELFCD, NELFE, SPT5). These proteins were fused to LEDGF-IBD and expressed in mouse LEDGF-/-MEF cells. The fusion proteins then target HIV integration to the chromatin binding sites. The HIV integration sites were identified using linker-mediated PCR and highthroughput sequencing and serve as surrogate for chromatin binding sites. Mapping was done using mouse genome mm9.