Chromatin reader that specifically recognizes and binds histone H3.3 trimethylated at 'Lys-36' (H3.3K36me3) and regulates RNA polymerase II elongation. Does not bind other histone H3 subtypes (H3.1 or H3.2). Colocalizes with highly expressed genes and functions as a transcription corepressor by modulating RNA polymerase II at the elongation stage (PubMed:24590075). Binds non-specifically to dsDNA (By similarity). Acts as a tumor-suppressor by repressing a transcriptional program essential for tumor cell growth (PubMed:24590075). Homooligomer; forms homooligomers via its C-terminus. Interacts with histone H3.3 trimethylated at 'Lys-36' (H3.3K36me3). Interacts (via MYND-type zinc finger) with NCOR1. Interacts (via MYND-type zinc finger) with MGA protein (via PXLXP motif). Interacts (via MYND-type zinc finger) with EZH2. Interacts with EMSY and E2F6. Interacts with PIAS1 and UBE2I (By similarity). Associates with chromatin and mitotic chromosomes. The PWWP domain specifically recognizes and binds histone H3.3 trimethylated at 'Lys-36' (H3.3K36me3) and adopts a five-bladed beta-barrel fold with an extended C-terminal alpha-helix, with a conserved H3.3K36me3-binding aromatic cage formed by Phe-291 and Trp-294 of the beta1-beta2 loop and Phe-310 of the beta3-beta4 loop. Specific recognition of H3.3 histone is mediated by the encapsulation of the H3.3-specific 'Ser 31' residue in a composite pocket formed by the tandem bromo-PWWP domains (PubMed:24590075). Ubiquitinated, leading to proteasomal degradation. Sumoylated following its interaction with PIAS1 and UBE2I. Truncated N-terminus.