Abstract: Objective To clone the gene encoding the novel colon cancer-associated antigen EID3 and investigate the possibility of using EID3 mRNA expression to diagnose patients with colon cancer.Methods Screening of a testis cDNA library using sera from patients with colon cancer led to discovery of the EID3 gene（NM_001008394.1），similar to tumor suppressor gene E1A.The pattern of EID3 mRNA expression was investigated in normal tissue and colon cancer cell lines using reverse transcription-PCR （RT-PCR）.Results The EID3 gene （1 002 bp） was cloned by PCR and overexpressed in E.coli at levels reaching 10% of total protein.The molecular weight was confirmed to be 39 kDa by SDS-PAGE and Western blot，and it was purified to 92% homogeneity.The gene encoding EID3 is located on chromosome 19q13.2，which contains one exon.RT-PCR analysis detected the gene in 39 of 43（90.7%） colon cancer cell lines，while EID3 mRNA was undetectable in all normal tissues examined except testis.Conclusions EID3 mRNA detection may prove to be a highly sensitive and specific technique to diagnose colon cancer.EID3 protein has been reported to initiate a humoral immune response in patients with colon cancer.Further studies are needed to explore the diagnostic potential of EID3 in colon cancer.

Key words: Colon cancer, EID3, Gene cloning, mRNA