Nobel Prize winner who identified reverse transcriptase, formulated the “Baltimore Classification” and laid the foundations for modern virology, PCR and antiviral drugs
Many of the greatest scientists in history will forever be remembered for breaking paradigms: Copernicus He will be remembered as the one who placed the sun at the center, and placed the earth in its humble place; Darwin – As someone who developed the idea of the evolution of species through natural selection; the priest Gregor Mendel He proposed laws of heredity that contradicted the biology known at the time. To these we can add the Einstein, Niels Bohr, Marie Curie, Alan Turing And others. Another such scientist walked among us until a few weeks ago, the Jewish-American biologist David Baltimore, who refuted the conventional wisdom in biology, who shook up the world of virology, in more ways than one – and life sciences could not go back once his discoveries were published. Baltimore, son-in-law Nobel Prize in Medicine In 1975, he passed away at the age of 87 in Massachusetts.
Baltimore was born on March 7, 1938, in Manhattan, the son of Gertrude, a psychologist, and Richard, a garment worker. His father was raised in a traditional home, and so, although his mother was a staunch atheist, he attended synagogue until his bar mitzvah. As a young man, he moved with his family to Great Neck, a suburb of New York City, where he attended high school. His early interest in biology led him to spend one of his summers at Jackson Laboratories, a private institute in Maine. There he also met an enthusiastic Jewish high school student named Howard Tamin (Temin), and the paths of the two will cross again in a big way.
Baltimore earned his undergraduate degree in biology at Swarthmore College, not the most prestigious or well-known institution at the time, but one that was and still is a warm home for Jewish students, at least according to some. But this private college has produced five Nobel Prize winners from its ranks over the years, one of whom would be Baltimore himself. He completed his studies in 1960, at which time he also met two young, ambitious researchers at the Massachusetts Institute of Technology (MIT), also of course Jewish – Salvador Luria Luria and Cyrus Levinthal.
Meet young researchers and leopards at the Massachusetts Institute of Technology. David Baltimore (right), Salvador Luria (left), and Nancy Hopkins, at MIT in 1973 | Source: US National Library of Medicine, Courtesy of the Massachusetts Institute of Technology. Museum
Backward progress
Like young faculty members today, Luria and Levintel took on the task of “scouting”: identifying outstanding students with research potential who could one day enroll in graduate and post-graduate studies at the prestigious institution. They identified the object of their search in Baltimore and invited him to MIT. Indeed, he soon found himself a doctoral student, but not at MIT, but in the laboratory of Professor Richard Franklin at Rockefeller University. His research there dealt with animal viruses.
In 1965, he joined on the recommendation of his colleague, Renato Dolbeco Dulbecco joined the Salk Institute in San Diego, which had been founded a few years earlier by Jonah Salk, the developer of the polio vaccine. A few years later he married Alice Huang, a Chinese-born virologist who also worked at the Salk Institute. They had one daughter.
In his early years as an independent researcher, Baltimore studied fairly conventional viruses, including polio. At some point, he became interested in viruses involved in the creation of cancerous diseases, especially in birds. These are now called “oncoviruses.” Baltimore, along with his young friend Howard Tamin, realized that they were facing a different type of virus, completely different from the known viruses. All the viruses then known replicated in a way that was then known (and sometimes mistakenly called “The central example of molecular biology"), according to which in the living world – including viruses, although they are not living in the ordinary sense of the word – messenger RNA molecules are produced as a copy of DNA in the cell nucleus. The messenger RNA then serves as instructions for building proteins. However, all the evidence that came from avian viruses showed the opposite direction, which was unthinkable: DNA molecules were created according to a template dictated by RNA. They called this surprising process "reverse transcription."
Baltimore and Tamin, along with a team led by Renato Dulbecco, concluded that the reverse transcription process is controlled by an enzyme they called “reverse transcriptase.”
Discovered viruses that make DNA from an RNA template. David Baltimore | Photo: NIH, via Wikimedia Commons
New worlds
The discovery of the enzyme and the entire process not only stunned the community of geneticists and molecular biologists, it also demanded a paradigm shift. Baltimore shouldered this task as well, dividing the entire world of viruses into six classes (later seven), each of which differs in its genome and the replication processes that govern it. This division is still called “Baltimore Classification"(Baltimore Classification), and the viruses that Baltimore and Tamin studied were named "Retroviruses“Over the years, drugs for viral diseases have been invented based on reverse transcriptase, which are based on inhibiting viral replication by blocking the action of this enzyme. Furthermore, it has been found to have applications inThe PCR device, as it allows the conversion of viral RNA into DNA, which in turn is replicated repeatedly until a level is obtained that allows for the identification and quantification of the viruses in the original sample.
From the moment Baltimore published his findings, he was on the fast track to receiving the Nobel Prize. Indeed, in October 1975, the prize committee announced that he would be awarded the prize jointly with Tamin and Dulbecco. Baltimore was the “Benjamin of the bunch,” having received the prize at only 37 years old—the age at which many researchers these days are just beginning their independent careers. Shortly after shaking hands with the King of Sweden, Baltimore moved on to his next research challenge. In addition to oncoviruses, cancer-causing viruses, many of which are members of the retrovirus family, another member of the group is The HIV virus, the cause of AIDS. The disease was at the center of public and research discourse in the 80s, and Baltimore became one of the most prominent figures in the study of the virus, its life cycle, and immune responses to it.
At the same time, in 1982, Baltimore was called to the forefront by philanthropist Jack Whitehead, who dreamed of establishing an independent research institute for basic biomedical research. Baltimore was indeed the right man for the task: within a short time the institute Established near MIT To this day, he is administratively linked to it, but not financially. The institute, which over the years has gone by its name, currently has only 19 faculty members. Several Israeli researchers have trained there over the years.
In 1982, Baltimore was named the flag by philanthropist Jack Whitehead. Whitehead Institute | Photo: Madcoverboy, CC BY-SA 3.0, Wikimedia Commons
A sad affair
Alongside the great success that characterized his years, his career was clouded by a sad episode that ended with a weak sigh. The year is 1986 when a colleague from Baltimore, Teresa Imanishi-Curry (Imanishi-Kari), who worked in another MIT lab, has been accused of the most serious charge. One of Teresa Imanishi-Kari’s postdoctoral fellows claimed that her paper—written with Baltimore and published in the journal Cell—was based on data that Imanishi-Kari had disbelieved. The complainant alleged serious flaws in the paper, which detailed how the immune system rearranges its genes to produce antibodies to substances that were new to her. In particular, her version of the results could not be reproduced in the lab, which was considered a breach of scientific trust of the highest order.
Baltimore stood on its hind legs and refused to recuse itself from the work. The postdoctoral fellow decided to withdraw her complaint, but it was already too late. The US National Science Foundation (NSF), which funded the study, decided to intervene and look into the issue in depth. The investigation turned into a congressional investigation headed by Congressman John Dingell, a veteran war fox who even involved the Secret Service – and who proceeded to conduct forensic identification on Imanishi-Curry's notebooks, no less.
About six years after the affair broke out, the Secret Service report was leaked to the media, and it clearly implicated Imanishi-Kari in the fabrication of the data. Baltimore did not know his soul about it, apologized and repented, and even gave up the high position he held at the time – president of Rockefeller University – and returned to MIT. In 1994, Imanishi-Kari was found guilty of 19 counts of scientific fraud, and she was given a heavy penalty of being denied research grants for the next decade.
But two years later, a surprising development occurred. Imanishi-Kari appealed the decision, and a panel convened at the federal Department of Health and Human Services decided to resoundingly acquit her of all charges. She returned to research at Tufts University. The entire affair, mistakenly called “The Baltimore Affair", clouded his career, but didn't stop it.
Retired from his position as president of Cal-Tech in 2006. David Baltimore (second from right) and Jet Propulsion Laboratory (JPL) staff | Photo: JPL, via Wikimedia Commons
There is something new in the West.
A year after the affair dropped from the headlines, Baltimore was appointed president of the California Institute of Technology, Caltech. At Caltech, Baltimore established another laboratory, which focused on two main research avenues: understanding the development and function of the immune system in mammals and studying the processes required to make the immune system more effective in resisting cancer. The second research avenue was based on a close acquaintance with a molecule called “MicroRNA“, a very small molecule that contains a short sequence of building blocks, and which, unlike messenger RNA, does not encode the production of a specific protein, but rather constitutes a kind of regulatory button or controller, which has the power to decide how much protein will be produced from each gene. Thus, it turned out that Baltimore and RNA never separated.
During his time at Caltech, which was much more relaxed, US President Bill Clinton awarded him the National Medal of Science. He retired from his position in 2006, but the laboratory continued to operate until 2019. In his final years, Baltimore fell ill with cancer, and on September 6, 2025, he passed away. His friends said that in addition to his scientific persona, he was a man of culture and conversation, who enjoyed wine and good food, a man of the great world. With his death, one of the great lights of molecular biology went out.
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Fascinating. I would like many more stories like this than the nonsense that saves the internet.
Fascinating, thanks for the article.