Disclosed is a polypeptide that includes amino acids 183-222 of CRIF, wherein the polypeptide does not include the full length CRIF1 amino acid sequence. Also disclosed is a nucleic acid molecule encoding this polypeptide, vectors including this nucleic acid molecule, and host cells transformed with these vectors. In some embodiments, methods are disclosed for treating a subject with cancer, comprising administering to the subject a therapeutically effective amount of an inhibitor of CDK12/CRIF1 interaction, thereby treating the cancer in the subject. In specific non-limiting examples, these methods can utilize CRIF1 polypeptides, nucleic acids encoding these polypeptides, and vectors including these nucleic acids.
