This video is a re-issue of the 100th episode of "This Week in Virology" from 2010, presented as a tribute to the late Dr. David Baltimore. The episode features an in-depth conversation with Baltimore, who reflects on his distinguished career and the evolution of virology. He recounts his early Ph.D. work in the 1960s, which led to the first characterization of a viral RNA-dependent RNA polymerase. He then details the logical progression that led to his Nobel Prize-winning discovery of reverse transcriptase in RNA tumor viruses, a finding that reshaped the central dogma of molecular biology and led to his eponymous virus classification system. Baltimore also discusses his pivotal role in the Asilomar conference on recombinant DNA, offers his perspective on major scientific paradigm shifts, and provides commentary on contemporary challenges like HIV vaccine development and the XMRV controversy. The conversation concludes with his advice for young scientists and personal reflections.
A Conversation with David Baltimore: Reflections on a Career in Virology
2:41 The Early Days of Virology: Baltimore explains his initial motivation in the 1960s was to use animal viruses as molecular probes to understand the biology of animal cells, much as bacteriophages were used to study bacteria.
7:33 Discovering Viral RNA Polymerases: He describes his Ph.D. work on Poliovirus and Mengovirus, which involved identifying the first RNA-dependent RNA polymerases. This discovery was crucial for understanding how RNA viruses, then considered a biological "anomaly," replicate their genomes without DNA.
12:40 Uncovering Negative-Strand Viruses: At his wife Alice's suggestion, he began working on Vesicular Stomatitis Virus (VSV). This led to the realization that it was a negative-strand virus, which logically implied it must carry its own polymerase inside the virion to initiate infection—a polymerase he subsequently discovered.
15:32 The Discovery of Reverse Transcriptase: Baltimore explains that RNA tumor viruses (retroviruses) did not fit his existing classification scheme. Influenced by Howard Temin's hypothesis that these viruses used a DNA intermediate to achieve stable cell transformation, he performed experiments that proved the existence of an RNA-dependent DNA polymerase (reverse transcriptase) within the virions in 1970.
17:29 The Baltimore Classification System: The discovery of reverse transcriptase provided the final piece of the puzzle, allowing him to formulate his comprehensive classification system. This system organizes all viruses based on the pathway their genome takes to produce messenger RNA (mRNA).
22:53 The Asilomar Conference on Recombinant DNA: As an organizer of the historic 1973 conference, Baltimore recounts how the scientific community came together to proactively address the safety and ethical concerns of new recombinant DNA technologies, establishing a framework that allowed the science to proceed responsibly.
33:50 Major Paradigm Shifts in Biology: When asked about the biggest conceptual shifts in his career, Baltimore identifies the discovery of messenger RNA as the most profound, followed by the discoveries of RNA splicing and microRNAs.
40:27 Challenges in Modern Virology—HIV and XMRV:
HIV: He explains that creating a vaccine is difficult because the virus evolves rapidly and has very few spikes, reducing the effectiveness of antibody binding. His lab's approach focuses on using gene therapy to program cells to produce protective antibodies.
XMRV: He expresses caution regarding the link between XMRV and chronic fatigue syndrome, drawing parallels to earlier, unproven claims about human cancer viruses. He stresses the need for rigorous science and satisfying Koch's postulates before offering treatments.
49:25 On Whether Viruses are Living: Baltimore considers viruses to be living because they are part of the living world, reproduce, and evolve. However, he views the question as primarily semantic and not critical for the scientific understanding of viruses.
52:51 Advice for Aspiring Scientists: He advises that one should only pursue a career in science if they "can't imagine yourself doing anything else," acknowledging its difficulty and the intense competition for funding.
1:03:25 Why Scientists Like Fishing: Baltimore concludes with a lighthearted reflection, suggesting that scientists enjoy fly fishing because it is a totally absorbing activity that requires constant calculation, concentration, and has an element of chance—much like scientific research.
Key Publications and Honors Mentioned
Poliovirus & Mengovirus Papers (1963): These two papers, referenced in the video description, detail Baltimore's Ph.D. research that first identified and characterized a viral RNA-dependent RNA polymerase, explaining how positive-strand RNA viruses replicate.
Viral RNA-dependent DNA Polymerase (1970): The summary provided references his landmark discovery of reverse transcriptase in RNA tumor viruses. This fundamentally altered the "central dogma" of molecular biology by showing that genetic information could flow from RNA back to DNA.
Nobel Prize in Physiology or Medicine (1975): He was awarded the prize jointly with Renato Dulbecco and Howard Martin Temin for "discoveries concerning the interaction between tumour viruses and the genetic material of the cell."
Minor Planet 73079 Davidbaltimore: The description notes that an asteroid discovered in 2002 at the Palomar Observatory was named in his honor.