To obtain the subject new factor, a protein having activity to control cell cycle and having a specific amino acid sequence, and useful as a reagent for screening antitumor substances, or as a therapeutic, preventive or diagnostic agent for various types of cancer.

This cell cycle control factor is a new protein (salt) having an amino acid sequence identical or virtually identical with one expressed by the formula. This protein or DNA coding is useful as a reagent for screening antitumor substances, or as a therapeutic, preventive or diagnostic agent for various types of cancer, gene diagnostic agent, etc., The antibody to this protein is useful as a diagnostic agent for diseases such as lung cancer and colon cancer. This cell cycle control factor is obtained by a process wherein mRNA is separated from a strain transduced with leucinophilicity by using Schizosaccharomyces, and using the mRNA, a cDNA library is prepared and then screened using a probe, and a DNA of the aimed cell cycle control factor obtained is expressed in host cells.