David Baltimore

David Baltimore is an American molecular biologist who, working independently of but at nearly the same time as Howard Temin, discovered the enzyme reverse transcriptase in 1970, an enzyme that certain viruses use to copy their genetic information from RNA back into DNA. The finding directly challenged the previously accepted central dogma of molecular biology, which held that genetic information flows in only one direction, from DNA into RNA and then into protein, and it explained how a whole class of RNA-based tumor viruses could permanently insert their genetic material into a host cell's own DNA. Reverse transcriptase later became one of the most important tools and objects of study in modern biomedicine, essential both to understanding retroviruses such as HIV and to a wide range of everyday genetic engineering and diagnostic laboratory techniques. Baltimore also developed an influential classification scheme, now called the Baltimore classification, that groups all viruses into a small number of categories based on how each type actually converts its genetic material into messenger RNA inside an infected cell. Baltimore shared the 1975 Nobel Prize in Physiology or Medicine with Renato Dulbecco and Howard Temin, and he later served as president of the California Institute of Technology and as founding director of the Whitehead Institute for Biomedical Research.