The CEACAM19 gene belongs to the CEACAM subfamily of the CEA gene family, which in turn belongs to the Immunoglobulin Superfamily (IgS) (Scorilas et al., 2003). It has a total length of 12,904 nucleotides and consists of 8 exons and 7 intervening introns (Scorilas et al., 2003). It is located downstream of the PVR gene (poliovirus receptor cell adhesion molecule) and upstream of the CEACAM16 gene at the chromosomal location 19q13.31.

CEACAM19 pre-mRNA is subjected to alternative splicing. According to UniProt, three main splice variants of the gene have been described. The first one, which is referred to as the "canonical" one, consists of 903 nt and encodes for a 300-amino-acid (aa) polypeptide chain (Scorilas et al., 2003). The second splice variant contains one more exon (exon 3) of 134 bp and encodes for a polypeptide chain of 142 aa residues (Scorilas et al., 2003). The third splice variant consists of 900 nt and encodes for a polypeptide chain of 299 aa residues. However, according to the Human Protein Atlas, another five splice variants have also been described.

Not identified so far.

The canonical polypeptide isoform that is encoded by the CEACAM19 gene (isoform 1) consists of 300 aa residues and has a putative molecular weight of 32.6 kDa. (Scorilas et al., 2003). This polypeptide corresponds to a protein with an N-terminal extracellular domain consisting of the aa residues 33-157 and one Ig-like helical transmembrane domain, similar to other members of the same gene family (CEA family), composed of the aa residues 158-178 (Scorilas et al., 2003). The protein carries a hydrophobic N-terminal sequence, which is thought to act as a signal peptide and which is comprised on its whole of the aa residues 1-32 (Scorilas et al., 2003). The signal peptide of the protein is removed. aa residues 179-300 represent the cytoplasmic part of this protein (Figure 1). The CEACAM19 protein bears no constant C2-like domains like the ones seen in other members of the same family (Beauchemin et al., 2013). The protein bears a 9-aa sequence (SAMGQRDIV - from position 92 to 100) that is present in the eIF5A domain of a variety of transcription factors in eukaryotes (Scorilas et al., 2003). Moreover, the CEACAM19 polypeptide is a heavily glycosylated glycoprotein, which carries an ITAM motif (Immunoreceptor Tyrosine-based Activation Motif) in its cytoplasmic tail (as most of the members of the same subfamily) (Beauchemin et al., 2013). Moreover, several putative sites for post-translational modifications, such as O-/N-glycosylation, phosphorylation, N-myristoylation, have been described (Scorilas et al., 2003).
The alternative splicing of CEACAM19 pre-mRNA leads to the production of two other protein isoforms. As described previously, the second splice variant encodes for a polypeptide of 142 aa residues, shorter than the one described as the canonical form of the protein. Besides the fact that the aa residues from position 143 to 300 are missing, this isoform also differs from the canonical one in that the glutamic acid residue in position 142 is replaced by an aspartic acid residue. The third protein isoform is derived from a splice variant of 900 nt and consists of 299 aa residues. In this case, the glutamine residue in position 282 of the canonical form is missing.
As described above, the Human Protein Atlas mentions the existence of another five splice variants of the CEACAM19 gene, which encode for secreted polypeptides and not transmembrane ones (contrary to the three main isoforms described earlier). Four of these polypeptides consist of 56 aa residues and share a common molecular weight of 6.1 kDa each, while one of them consists of 54 amino acids and has a molecular weight of 6 kDa. All these polypeptide chains bear a signal peptide consisting of the amino acids 1-33.

The CEACAM19 gene is widely expressed in a variety of tissues. Based on RNA-seq experiments (Fagerberg et al., 2014), higher expression levels are mainly seen in skin and testis. However, moderate to high expression levels have also been described in the prostate, adrenal gland, endometrium, lung, and ovary.

The three main CEACAM19 protein isoforms that bear a transmembrane domain are characterized as single-pass type-I membrane proteins. These are proteins that traverse the membrane only once with their N-terminal domain on the extracellular side of it and their signal peptide being removed. However, according to the Human Protein Atlas, the rest of the protein isoforms, which lack transmembrane domains, are predicted to be secreted.

The functions of the CEACAM19 protein (either physiological or pathological) have not been elucidated, yet.