Spans 120 Kb of genomic DNA and consists of 24 exons transcribed into a mRNA that undergoes alternative splicing (Marango et al., 2007).

Undergoes complex alternative splicing. Most primary trancripts splice directly to exon 3, which contains the proper translation initiation site, though small fraction of transcripts retain upstream sequence including exons 1 and 2 (Keats et al., 2005).

Alternative splicing of exon 4 to 4a instead of 5 generates de MMSET III protein (273 amino acids, 32 kDa), due to the presence of an in-frame stop codon in exon 4a. Alternative splicing of exon 10 to 11 or 12 generates MMSET I (647 amino acids, 75 kDa) or the full-length MMSET II (1365 amino acids, 155 kDa) respectively, due to the presence of an in-frame stop codon in exon 11. A third transcript initiated within a middle intron of MMSET, encoding a mRNA comprising the 3half of MMSET gene was identified and encodes a protein named RE-IIBP.
The long transcript, MMSET II, contains: 2 PWWP (proline-tryptophan-tryptophan-proline) domain, a HMG box (high mobility group), 4 PHD (plant-home domain)- type zinc finger motifs and a SET domain. MMSET I contains only a PWWP and a HMG domain and REIIBP, 2 PHD, a PWWP and a SET domain (Keats et al., 2005).

Widely expressed.
It is expressed preferentially in rapidly growing embryonic tissues, in a pattern corresponding to affected organs in WHS patients (Stec et al., 1998). Recently it has been shown that MMSET is highly expressed in different tumor types such as carcinomas of the gastrointestinal tract (stomach, colon, anal canal), small cell lung carcinoma, bladder, female genitals and skin (Hudlebusch et al., 2011). It is also highly expressed and associated with aggressive neuroblastoma (Hudlebusch et al., 2011).

Homogenous pattern within the nucleus, excluded from the nucleolus.

Histone methyltransferase that leads to dimethylation of histone 3 lysine 36 (H3K36) (Marango et al., 2008; Martinez-Garcia et al., 2011; Kuo et al., 2011). WHSC1 is involved in the cellular response to DNA damage through its activity on H4K20 residue (Hajdu et al., 2011; Pei et al., 2011).