David Baltimore

David Baltimore, born in 1938, American molecular biologist and Nobel laureate. Baltimore researched the action of tumor viruses on the genetic structure of the cells they infect. For his work on the relationship between genetics and tumor viruses, Baltimore shared the 1975 Nobel Prize in physiology or medicine with Italian-born American virologist Renato Dulbecco and American virologist Howard M. Temin.

Baltimore was born in New York City. After earning a B.S. degree in chemistry in 1960 from Swarthmore College, he began his graduate studies in biology at the Massachusetts Institute of Technology (MIT). In 1961 he transferred to Rockefeller University, from which he received a Ph.D. degree in 1964. Baltimore was a postdoctoral fellow at MIT from 1963 to 1964, at the Albert Einstein College of Medicine from 1964 to 1965, and at the Salk Institute for Biological Studies from 1965 to 1968. At the Salk Institute he worked with Dulbecco, who was developing techniques to differentiate normal cells from cells that had become tumor cells due to viruses. In 1968 Baltimore was appointed associate professor of microbiology at MIT, and in 1972 he was named a full professor there. In 1983 Baltimore became director of the Whitehead Institute, a newly established independent biological research institute in Boston, Massachusetts, closely affiliated with MIT. He returned to Rockefeller University as president in 1990.

Baltimore was forced to resign Rockefeller's presidency in 1991 after he lost the support of the university faculty and trustees following a scandal involving a paper he had written in 1986 with a Tufts University professor. A graduate student at Tufts accused the Tufts professor of fabricating data presented in the paper. Although Baltimore himself was never accused of data falsification, investigations by several government bodies and a committee of the United States House of Representatives found that the graduate student's charges were credible. But in 1996, ten years after the paper in question was published, a federal appeals panel rejected the fraud charges made against the Tufts professor. One year later, Baltimore was appointed president of the California Institute of Technology.

Since 1953, when James Watson and Francis Crick revealed the structure and mechanism of deoxyribonucleic acid (DNA), a central tenet of molecular biology had been that DNA transmits genetic information through ribonucleic acid (RNA). Virtually no one believed that RNA could transmit genetic information to DNA. However, in 1965 Howard Temin, an assistant professor of oncology at the University of Wisconsin, proposed that in some viruses, RNA changed the DNA of its host cell by inserting its own genes, a process known as reverse transcription. Temin's proposal was widely derided, but he held to the idea of reverse transcription. Baltimore, working along similar lines at MIT, remained uncommitted to one view or the other but investigated Temin's notion. In 1970, while studying the Rauscher mouse-leukemia virus, Baltimore found an example of an RNA viral enzyme that copies genetic information to the host cell's DNA. At the same time, Temin found a similar enzyme in the Rous sarcoma virus. Both researchers called this enzyme RNA-directed DNA polymerase; it later became known as reverse transcriptase. Viruses that use this method of altering a host's DNA are called retroviruses. The human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome(AIDS), is a well-known retrovirus. The discovery of reverse transcriptase shed new light on the mechanism by which a normal cell is changed to a cancer cell. Normal cells can monitor their own growth relative to other cells and halt replication when a cell meets its neighbors. A retrovirus destroys this mechanism, and runaway growth is the result. Several strategies for treating cancer and AIDS rely on the findings of Baltimore and Temin.