DNA size is 4081 bp with 6 exons. CBX7 is a highly conserved gene in chimpanzee, dog, cow, rat and mouse.

mRNA size: 3964 bp.

251 amino acids.
Isoelectric point: 10,0228.
Molecular weight of the protein: 28209 Da.

CBX7 has a chromodomain region which is commonly found in proteins associated with the remodelling and manipulation of chromatin. In mammals, chromodomain-containing proteins are responsible for aspects of gene regulation related to chromatin remodelling and formation of heterochromatin regions. Chromodomain-containing proteins also bind methylated histones and appear in the RNA-induced transcriptional silencing complex. Specifically, CBX7 is involved in maintaining the transcriptionally repressive state of its target genes. The better characterized target of CBX7 is the INK4a/ARF locus, which is repressed by CBX7 in order to overcome the senescent phenotype in several mouse and human cell lines. Repression of other targets like E-cadherin has been also suggested.

CBX7 is expressed ubiquitously, but at higher levels in the nervous system, thyroid gland, prostate, fallopian tubes and bladder in normal tissue. CBX7 expression is also high in ES cells.

In the nucleus.

CBX7 is a member of the Polycomb group (PcG) genes, which are transcriptional repressors that play an essential role in development, cancer progression and stem cell maintenance. Mainly two different PcG complexes have been described: Polycomb Repressive Complex 1 (PRC1) and PRC2. PRC2 is the complex implicated in initiating the silencing of its target genes by methylating histone H3 on lysines 9 and 27. PRC1 is implicated in stabilizing this repressive state by recognizing the methylation marks through the Polycomb proteins and by ubiquitinating the histone H2A on Lys119. CBX7 belongs to the PRC1 complex and has been described to be a regulator of cellular lifespan by repressing the INK4a/ARF locus in several mouse and human cell lines. On the other hand, depletion of CBX7 from the cell induces a senescent phenotype by increasing the expression of the cell cycle regulators p16/ARF.
X chromosome inactivation
CBX7 has high affinity for binding H3K9me3 and H3K27me3. It associates with heterochromatin, binds RNA and its enriched in the X chromosome, giving CBX7 a role in maintaining the repression of genes in the X chromosome.
Epigenetic regulation
CBX7, as part of the PRC1 complex, has a role in maintaining the repressive state of its target genes. CBX7 binds to the long non-coding RNA ANRIL in order to represses the INK4a/ARF locus and this interaction is essential for CBX7s function. Both CBX7 and ANRIL have been found to have high levels in prostate cancer tissues.
Stem cells self-renewal
CBX7 has been recently implicated to be essential for maintaining the pluripotency state of stem cells (ES cells). Overexpression of CBX7 in ESC impairs cell differentation. On the other hand, depletion of CBX7 from ESC induces spontaneous differentiation. Two different miR families (miR-125 and miR-181) were identified in a screening for CBX7 regulators and have been described to have a role in ESC differentiation by targeting the 3UTR of CBX7.

Expression of CBX7 without the Pc box or with point mutations in the chromodomain region (F11A, K31A, W32A, W35A) does not extend the life span of human or mouse cells. The mutant R17Q, which affects the binding of CBX7 to RNA, extended the lifespan of cells, but to a lesser extent than CBX7 wt. Point mutations in the Pc box as F234D or F244D result in loss or reduced interaction of CBX7 with RNF2.