Polycomb group (PcG) protein that specifically recognizes and binds mono- and dimethyllysine residues on target proteins, thereby acting as a 'reader' of a network of post-translational modifications. PcG proteins maintain the transcriptionally repressive state of genes: acts as a chromatin compaction factor by recognizing and binding mono- and dimethylated histone H1b/H1-4 at 'Lys-26' (H1bK26me1 and H1bK26me2) and histone H4 at 'Lys-20' (H4K20me1 and H4K20me2), leading to condense chromatin and repress transcription. Recognizes and binds p53/TP53 monomethylated at 'Lys-382', leading to repress p53/TP53- target genes. Also recognizes and binds RB1/RB monomethylated at 'Lys- 860'. Participates in the ETV6-mediated repression. Probably plays a role in cell proliferation. Overexpression induces multinucleated cells, suggesting that it is required to accomplish normal mitosis. {ECO:0000269|PubMed:17540172, ECO:0000269|PubMed:18408754, ECO:0000269|PubMed:20870719, ECO:0000269|PubMed:20870725}. This is the function of Ensembl gene identifier ENSG00000185513 (L3MBTL1, L3MBTL histone methyl-lysine binding protein 1).