A method for treatment of a disease or condition in an organism characterized by an abnormal level of interaction between a BLM domain and its natural binding partner is described. The disease or condition may also be characterized by an abnormality in a signal transduction pathway, wherein the pathway contains a protein with a BLM domain. The method includes disrupting or promoting that interaction (or signal) in vivo. The method also involves inhibiting the activity of the complex formed between the BLM domain-containing protein and its natural binding partner. A method for diagnosis of such a disease or condition by detecting the level of such interaction as an indication of that disease or condition is also described. Also, a method for screening for an agent useful for treatment of such a disease or condition by assaying potential agents for the ability to disrupt or promote that interaction is described. The invention also features a peptide comprising, consisting or consisting essentially of a BLM domain.