Chromatin reader protein that recognizes and binds histone H3 trimethylated at 'Lys-9', dimethylated at 'Lys-27' and trimethylated at 'Lys-27' (H3K9me3, H3K27me2 and H3K27me3, respectively) (PubMed:12947414). Part of multimeric repressive chromatin complexes, where it is required for transmission and restoration of repressive histone marks, thereby preserving the epigenetic landscape (PubMed:12947414). Required for chromatin targeting and maximal enzymatic activity of Polycomb repressive complex 2 (PRC2); acts as a positive regulator of PRC2 activity by bridging the pre-existing histone H3K27me3 and newly recruited PRC2 on neighboring nucleosomes (By similarity). Acts as a corepressor for REST by facilitating histone-lysine N-methyltransferase EHMT2 recruitment and H3K9 dimethylation at REST target genes for repression (By similarity). Involved in X chromosome inactivation in females: recruited to Xist RNA-coated X chromosome and facilitates propagation of H3K9me2 by anchoring EHMT2 (PubMed:24144980). Promotes EZH2 accumulation and H3K27me3 methylation at DNA double strand breaks (DSBs), thereby facilitating transcriptional repression at sites of DNA damage and homology-directed repair of DSBs (By similarity). Required for neuronal migration during brain development by repressing expression of RHOA (PubMed:28076783). By repressing the expression of SCN8A, contributes to the inhibition of intrinsic neuronal excitability and epileptogenesis (PubMed:28842554). In addition to acting as a chromatin reader, acts as a hydro-lyase (By similarity). Shows crotonyl-coA hydratase activity by mediating the conversion of crotonyl-CoA ((2E)-butenoyl-CoA) to beta-hydroxybutyryl-CoA (3-hydroxybutanoyl-CoA), thereby acting as a negative regulator of histone crotonylation (By similarity). Histone crotonylation is required during spermatogenesis; down-regulation of histone crotonylation by CDYL regulates the reactivation of sex chromosome-linked genes in round spermatids and histone replacement in elongating spermatids (PubMed:28803779). By regulating histone crotonylation and trimethylation of H3K27, may be involved in stress-induced depression-like behaviors, possibly by regulating VGF expression (PubMed:30665597). May have histone acetyltransferase activity; such activity is however unsure in vivo (PubMed:12072557). Not able to recognize and bind histone H3K9me3, histone H3K27me2 and histone H3K27me3, due to the presence of a N-terminal extension that inactivates the chromo domain. acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] 3-hydroxybutanoyl-CoA = (2E)-butenoyl-CoA + H2O Forms multimers and multimerization is required for stable binding to chromatin (By similarity). Interacts with HDAC1 and HDAC2 via its C-terminal acetyl-CoA-binding domain (PubMed:12947414). Interacts with EZH2, EED, SUZ12, REST, EHMT1 and EHMT2 (By similarity). Part of a complex containing at least CDYL, REST, WIZ, SETB1, EHMT1 and EHMT2 (By similarity). Part of a complex containing at least CDYL, MIER1, MIER2, HDAC1 and HDAC2 (By similarity). Interacts with CHAF1A and CHAF1B; bridging the CAF-1 complex to the MCM2-7 (MCM) complex (By similarity). Interacts with MCM3 and MCM5; bridging the CAF-1 complex to the MCM2-7 (MCM) complex (By similarity). Interacts with EHMT2 and PRDM9; interaction only takes place when PRDM9 is bound to hotspot DNA (PubMed:27932493). Recognizes and binds histone H3 trimethylated at 'Lys-9', dimethylated at 'Lys-27' and trimethylated at 'Lys-27' (H3K9me3, H3K27me2 and H3K27me3, respectively) on chromatin (PubMed:24144980). Multimerization is required for chromatin-binding (By similarity). Recruited to Xist RNA-coated X chromosome (PubMed:24144980). Recruited to sites of DNA double strand breaks in a PARP1-dependent fashion (PubMed:29177481). Highly expressed in testis (at protein level) (PubMed:10192397). Expressed in the hippocampus (at protein level) (PubMed:28842554). Expressed in the medial prefrontal cortex, prelimbic cortex, intralimbic cortex and cingulate cortex area (at protein level) (PubMed:30665597). Isoform 1: Expressed as 2 transcripts encoding the same protein, a ubiquitous transcript and a highly expressed testis-specific transcript (PubMed:10192397). Highly expressed in elongating spermatids during histone hyperacetylation. Down-regulated upon neuronal activity in the hippocampus (PubMed:28842554). Up-regulated after social defeat stress (PubMed:30665597). The chromo domain recognizes and binds histone H3K9me3, histone H3K27me2 and histone H3K27me3. The acetyl-CoA-binding domain mediates crotonyl-coA hydratase activity (By similarity). The acetyl-CoA-binding domain is required for recruitment to sites of DNA double strand breaks and for binding to poly (ADP ribose) moieties (By similarity). Mice show no overt differences in body weight, but males display a substantial decrease in the size and weight of the testis and show reduced fertility. Males show decreased epididymal sperm counts, sperm cell motility, and sperm velocity and a marked increase in cell apoptosis in the testis. Interaction with HDAC1 or HDAC2 prevents coenzyme A binding. Was initially reported to display histone acetyltransferase activity, with a preference for histone H4 (PubMed:12072557). Such activity is however unsure in vivo. Histone acetyltransferase activity would be in contradiction with the function of the protein in corepressor complexes (PubMed:12947414). Moreover, crystallographic studies in human demonstrated that it does not share any similarity with other acetyltransferases and instead forms a crotonase-like fold.