Chromatin reader involved in the silencing of endogenous retroviruses (ERV) class-I elements, such as LTR12 (PubMed:37938770). Specifically binds histone H3 trimethylated at 'Lys-9' (H3K9me3) deposited by SETB1 at class-I ERV and directly mediates recruitment of corepressor complexes, such as Sin3-type and N-Cor complexes, leading to ERV silencing (PubMed:37938770). . This is the function of TNRC18 (trinucleotide repeat containing 18, Ensembl gene identifier ENSG00000182095).