CAGE1, also known as CT3; CT95; CTAG3; bA69L16.7, is a 639-amino acid protein. It shares 76% sequence identity with a monkey homolog. RT-PCR analysis detected testis-specific expression among normal tissues and wide expression among various cancer tissues and cancer cell lines including those from cervical, melanoma, hepatic, renal, myeloma, and breast cancers. CTAG3 was overexpressed in cancer tissues compared with surrounding noncancerous tissues. Transfection experiments with a GFP-CTAG3 construct indicated a predominantly nuclear localization.