A subset of xeroderma pigmentosum (XP) group E cells lack a factor of the UV-damaged DNA binding activity. Both 127 kDa and 48 kDa proteins have been reported to be responsible for the binding activity. A cDNA for the 127 kDa UV-damaged DNA-binding protein (p127-Ddb1) was isolated from a mouse fetal brain full length-enriched cDNA library, and an open reading frame of 1140 amino acids was identified. Reverse transcription-coupled polymerase chain reaction (RT-PCR) showed that mouse Ddb1 messenger is ubiquitously expressed in adult tissues as well as in embryo's. The gene was mapped to near the public locus D19Mit22 region of mouse chromosome 19.