RNA polymerase II (Pol II) is an enzyme that is composed of twelve subunits and is responsible for the transcription of protein-coding genes. Transcription initiation requires Pol II-mediated recruitment of transcription machinery to a target promoter, thereby allowing transcription to begin. The integrator complex is a multi-protein complex that associates with the C-terminal domain of Pol II and is involved in small nuclear RNA (snRNA) transcription and 3’-end processing. INTS3 (integrator complex subunit 3), also known as INT3 or SOSS-A, is a 1,043 amino acid nuclear protein and is a subunit of the Integrator complex, which associates with the C-terminal domain of RNA polymerase II large subunit and mediates 3-prime end processing of small nuclear RNAs U1 and U2. Expressed in the nucleus, INTS3 exists as four alternatively spliced isoforms and is encoded by a gene located on human chromosome 1q21.3.