The present invention provides a human polypeptide homolog of DBF4/ASK1 (for "Activator of S phase kinase") and polynucleotides which identify and encode DRF1 (for "DBF4 Related Factor 1"). In addition, the invention provides expression vectors, host cells and methods for its production. The invention also provides methods for the identification of DRF1 or DRF1-containing complex agonists/antagonists, useful for the treatment of human diseases and conditions.