Previously, we have reported a novel protein, D40, that specifically binds to a nuclear factor GCF by two-hybrid system. Northern analysis on tumor cell lines revealed that mRNA of D40 is about 5 kb. To get cDNA clones that cover the total coding region of D40 protein, approximately 5 x 10(5) clones of a human cDNA library were screened, and then several positive clones were obtained. RACE was performed to get the 5' end of the cDNA. DNA sequencing revealed an open reading frame that encodes a protein with 887 amino acids. in vitro transcription and translation analysis of D40 revealed that the molecular weight of the protein is 110 to approximately 130 kda.