4193 bp

DDB1: 1140 amino acids, 127 kDa; DDB2: 427 amino acids, 48 kDa; DDB1 (p127) and DDB2 (p48) form a stable heterodimer UV-DDB

The damage-specific DNA binding (UV-DDB) activity purified as a heterodimer (p127 and p48) is expected to play a role in damage recognition prior to the Nucleotide Excision Repair (NER) because the DDB protein is reported to recognize many types of DNA lesions and is inducible by treatment with DNA-damaging agents. After UV irradiation, dynamic nuclear accumulation of DDB1 from the cytoplasm was found after 24 h. The function of the gene product is not completely clarified yet. Band shift assays suggested that the XPE gene product acts as a damaged DNA binding protein (DDB), with high affinity to UV-induced 6-4Pyrimidine-Pyrimidone photoproducts. However, defective DDB binding activity is not a common feature of XPE mutant cell lines and in fact two (or even more) proteins may be involved in the binding activity: p48 and p125. In cells from several XPE patient mutations in p48 have been found but so far no mutations have been found in the p125 gene. XPE patients show mild dermatological symptoms and cells from these patients have a relatively high repair capacity. XPE cells are not necessarily defective in repair: p125 is proposed to play a role in opening up chromatin to make CPD accessible to the NER machinery, but is not required for repair of 6-4PP. Interestingly, cell lines and primary tissues from rodents are fully deficient in the expression of the p48 protein . This explains the absence of GGR of CPD in these cells. Exogenous expression of p48 in hamster cells confers enhanced removal of CPD from genomic DNA and nontranscribed strand of active genes. The p48 protein is upregulated by p53.

three single base substitutions only in DDB2 (p48) gene