A polypeptide possessing an action of causing chromatin condensation; a sense nucleic acid encoding the polypeptide; an antisense nucleic acid thereof, a probe or primer capable of specifically binding to the nucleic acid; an antibody or a fragment thereof against the polypeptide; an agent for controlling apoptosis, comprising the nucleic acid, the polypeptide, or the antibody or a fragment thereof; a screening method for a substance for controlling chromatin condensation, comprising evaluating an activity of causing chromatin condensation exhibited by the polypeptide; and a substance for controlling chromatin condensation. The present invention is useful for screening a substance controlling apoptosis, its use for controlling apoptosis and its applications to various diseases accompanying apoptosis.