Monoclonal antibody (MAb) 1C5 reacts with 87% of uterine cervical adenocarcinoma and bovine beta -casein, but not with squamous cell carcinoma. To clarify the characteristics of the antigen (beta -casein-like protein; BCLP) recognized by MAb 1C5, molecular cloning was performed using 5 ' rapid amplification of the cDNA ends (5 ' RACE) and the oligo-capping method. The protein predicted from the cDNA consisting of 937 nucleotides comprises 222 amino acids. The BCLP gene and deduced amino acid sequences were novel and showed no similarity to known cancer-associated genes in the database. Northern blot analysis showed that a 1.1 kb transcript was ubiquitously expressed in cancer cell lines and was predominantly expressed in uterine cervical adenocarcinoma. To clarify the function of BCLP, BCLP cDNA was transfected into L929 cells, resulting in a significant increase in cell area, a downregulation of cell growth rate and a decrease in cell attachment. We conclude that BCLP might be associated with cell morphology and a regulation of growth pattern of tumor.