NSD3 was first described in 2000, by studying the PWWP (proline-tryptophan-tryptophan-proline) domain of NSD2 and performing a database search for proteins having the PWWP domain in their structure. NSD3 protein is found on chromosome 8p11.2 [
12], encoding three isoforms by alternative splicing. A protein of 1437 amino acids, termed NSD3L or long isoform [
13]. Alternative splicing of exon 10 encodes a protein of 645 amino acids, named NSD3 short (NSD3S), which is identical to NSD3L on the first 619 amino acids [
12]. Finally, isoform WHISTLE (WHSC1-like 1 isoform 9 with methyltransferase activity to lysine), a short alternative splice version of the C- terminal of NSD3L that encodes a protein of 506 amino acids. In relation to the protein domains found in NSD3L, it has 5 PHD (plant-homeodomain)-type zinc fingers motifs, 2 PWWP domain, and the methyltransferase SET domain. Right next to the SET domain, there is a SAC (SET-associated Cys-rich) domain rich in cysteines, and finally, near the end of the C-terminal of the protein there is a Cys-His-rich domain termed C5HCH motif [
13,
14]. The PWWP domain is a histone methyl-lysine (H3K36) reader, acting as an epigenetic regulator of gene expression [
15,
16,
17], and postulated as a site for protein-protein interactions, due to the amino acid composition [
18]. The PHD domain is relevant for binding chromatin at histone H3 lysine 4 unmodified or methylated [
19]. The SET domain is a region conserved between the SET family of methyltransferases, with specificity for mono or di-methylation of H3 lysine 36. The SET domain is separated into 3 smaller segments, the pre-SET, SET and post-SET domain, all of them needed for the catalytic activity [
20], importantly the post-SET region is essential for binding to nucleosomes [
21]. Finally, the PHD5-C5HCH region of NSD3 recognizes the H3 N-terminal peptide containing unmodified K4 and trimethylated K9, this recognition may vary from the one for NSD1 and NSD2 and may localize this H3K36 methyltransferases to different genome sites [
14]. As NSD3S encodes only the N-terminal of the full-length protein, it only has the first PWWP domain, and lacks the methyltransferase activity [
12,
13] (
Figure 1). In relation to the amino acid sequence, it reveals a similarity of 68% with NSD1 and 55% with NSD2, in regions with conserved domains (between residues 703 and 1409), including the SET domain [
13].