In the genome, MUC16 is localized in 19p13.2 chromosome and is coded by sequences present within approximatively 179kb of genomic DNA.

As per the present available information, there is a discrepancy regarding the total number of exons present in MUC16 genomic DNA. This discrepancy is due to the absence/presence of some of the genomic sequences (particularly for the repeat regions) in the available genomic databases. The terminal nine exons on both 5 and 3 ends code for the amino- and carboxy-terminal domains of MUC16, respectively. At the same time, it has been proposed that five consecutive exons code for a single repeat unit (SRU) of the central tandem repeat domain.

MUC16 protein harbors a central tandem repeat region, N-terminal domain and carboxy terminal domain. The N-terminal domain has 12070 numbers of amino acids rich in serine/threonine residues and accounts for the major O-glycosylation known to be present in CA125. The MUC16 protein back bone is dominated by tandem repeat region, which has more than 60 repeat domains, each composed of 156 amino acids. Though all the individual repeat units are not similar, most of them occur more than once in the sequence.
The repeat units are rich in serine, threonine and proline residues, which are typical for any mucins. Each repeat unit has some homology to the SEA (Sea-urchin sperm protein, Enterokinase and Agrin) module, whose exact biological function is not known.
The epitopes for known anti-CA125 antibodies (OC125 and M11) are thought to be present on a small cysteine ring region present in the tandem-repeat region of MUC16.
The carboxy-terminal domain has 284 aminoacids and can be divided into three different regions: extra cellular, transmembrane and cytoplasmic tail. The extracellular part of the carboxy-terminal domain has many N-glycosylation sites and some O-glycosyaltion sites. Several in silico analyses suggest a putative cleavage site in the extracellular part of carboxy-terminal domain. The MUC16 cytoplasmic tail is 31 amino acids long and has many possible phosphorylation sites.
The phosphorylation of CA125 in WISH cells has been reported by labeling with 32PO43- and immunoprecipitaion analysis but the exact site of phosphorylation is yet to be mapped. Interestingly, CA125 contains a putative tyrosine phosphorylation site (RRKKEGY), which was first recognized in Src family protein. This sequence is conserved in the translated mouse EST (AK003577) that has homology with CA125/MUC16 at the C-terminal end. Recently, it has been shown that MUC16 cytoplasmic tail, which contains a polybasic aminoacid sequence, interacts with cytoskeleton through ERM (ezrin/radixin/moesin) actin-binding proteins.

The expression of MUC16 has been reported in human epithelia of conjunctiva, cornea, middle ear and trachea under normal physiological conditions. MUC16 is also expressed in ovarian carcinoma.

It is a type I membrane-bound protein and due to cleavage gets secreted into the extracellular space. On the ocular surface, MUC16 is expressed on the tips of the microplicae of the ocular surface.

MUC16 provides a disadhesive protective barrier to the ocular epithelial surface. Overexpression of CA125/MUC16 in ovarian cancer indicates its possible role in cancer pathogenesis. Studies have shown that CA125/MUC16 binds to mesothelin and galectin-1, which are overexpressed in ovarian cancer. It has also been shown that mesothelin-MUC16 interaction has significance in adhesion of ovarian cancer cells to mesothelial cells present on the inner wall of the peritoneum and on the surface of other abdominal organs. This cell to cell adhesion may help in ovarian cancer metastasis. It has been proposed that galectin-1 bound to MUC16 may cause apoptosis of T cells, and thus help in the suppression of the host immunity.

Similar to mucin 16 of Pan troglodytes, Canis lupus familiaris, Mus musculus, Rattus norvegicus and Gallus gallus.