Is a negative regulator of Notch target genes expression, required for RBPJ-mediated transcriptional repression (PubMed:29030483). It recruits KDM1A to Notch-responsive elements and promotes KDM1A-mediated H3K4me demethylation (PubMed:29030483). Involved in the regulation of ubiquitin-dependent degradation of a set of methylated non-histone proteins, including SOX2, DNMT1 and E2F1. It acts as an adapter recruiting the CRL4-DCAF5 E3 ubiquitin ligase complex to methylated target proteins (PubMed:29691401, PubMed:30442713). Required for normal maturation of myeloid progenitor cells (By similarity). {ECO:0000250|UniProtKB:Q8BLB7, ECO:0000269|PubMed:29030483, ECO:0000269|PubMed:29691401, ECO:0000269|PubMed:30442713}. This is the function of L3MBTL3 (L3MBTL histone methyl-lysine binding protein 3, ENSG00000198945).