PTASHNE, MARK STEPHEN

PTASHNE, MARK STEPHEN (1940– ), U.S. biochemist. Born in Chicago, Ptashne graduated with a B.S. from Reed College in Portland, Oregon, and received his Ph.D. from Harvard University under the direction of Matthew Meselson. He joined the faculty of biochemistry and molecular biology at Harvard (1965) where he became professor (1971), chairman (1980–83), and Herschel Smith Professor from 1993. He was later a faculty member of the Molecular Biology Program at Memorial Sloan-Kettering Cancer Center, New York. His early research concerned the relationship between a virus called phage lambda and the bacteria it infects. There are two possible outcomes to infection. The virus may multiply and destroy the infected bacteria, a process termed lysis. Alternatively, the viral genetic information may persist without destroying the bacteria, a process called "lysogeny." However the quiescent phage DNA may subsequently be reactivated and lead to bacterial lysis. Ptashne identified and characterized the protein which determines the outcome of infection and he elucidated the mechanisms by which it operates. These discoveries were the basis for the new field of "transcriptional regulation" which explores the control of genetically determined programs in cells. It has crucially important implications for understanding the molecular basis of normal development and the abnormal events underlying cancer. He continued to work on gene regulation in normal and cancer cells. He reviewed his research in A Genetic Switch: Phage Lambda Revisited (20043). His work has been recognized by many honors, including election to the U.S. National Academy of Sciences, the Gairdner Award (1985) and the Lasker Award for Basic Medical Science (1997). Ptashne is an accomplished violinist. (Michael Denman (2nd ed.)