Joshua Lederberg and Norton Zinder report on transduction, or transfer of genetic information to cells by viruses. They show that a phage of Salmonella typhimurium can carry DNA from one bacterium to another.

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Joshua Lederburg Collection

Interview with Joshua Lederberg - (requires ISDN+ modem and RealPlayer)

Bacterial Variation Since Pasteur, ASM News 58, 1992. p.261 [pdf]

Alfred Hershey and Martha Chase suggest that only DNA is needed for viral replication. Using radioactive isotopes 35S to track protein and 32P to track DNA, they show that progeny T2 bacteriophage isolated from lysed bacterial cells have the labeled nucleic acid. Further, most of the labeled protein doesn’t enter the cells but remains attached to the bacterial cell membrane.

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The Hershey-Chase Experiments

Hershey, A. D. and M. Chase. 1952. Independent functions of viral protein and nucleic acid in growth of bacteriophage. J. Gen. Physiol. 36: 39-56. In Microbiology: A Centenary Perspective, edited by Wolfgang K. Joklik, ASM Press. 1999, p. 474 [pdf]

Francis Crick and Maurice Wilkins, together with James Watson, describe the double-helix structure of DNA. The chemical structure is based on X-ray crystallography of DNA done by Rosalind Franklin. Crick, Wilkins and Watson are awarded the Nobel Prize in Medicine or Physiology in 1962.

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DNA Helix Turns 40, ASM News 60,1994. p.28 [pdf]

Peter Mitchell proposes the chemiosmotic theory, in which a molecular process is coupled to the transport of protons across a biological membrane. He argues that this principle explains ATP synthesis, solute accumulations or expulsions, and cell movement (flagellar rotation). Mitchell is awarded the Nobel Prize in Chemistry in 1978.

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Peter Mitchell and the Chemiosmotic Theory, ASM News 63, 1997. p.13 [pdf]

Francois Jacob, David Perrin, Carmen Sanchez and Jacques Monod propose the operon concept for control of bacteria gene action. Jacob and Monod later propose that a protein repressor blocks RNA synthesis of a specific set of genes, the lac operon, unless an inducer, lactose, binds to the repressor. With Lwoff, Jacob and Monod are awarded the Nobel Prize in Medicine or Physiology in 1965.

Marshall Nirenberg and J.H. Matthaei observe that a synthetic polynucleotide, poly U, directs the synthesis of a polypeptide composed only of phenylalanine. They conclude that the nucleotide base triplet UUU must code for phenylalanine. This is the start of successful efforts to decipher the genetic code. With Robert Holley and Har Gobind Khorana, Nirenberg is awarded the Nobel Prize in Medicine or Physiology in 1968.

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Marshall Nirenberg Collection

Sydney Brenner, Francois Jacob and Matthew Meselson use phage-infected bacteria to show that ribosomes are the site of protein synthesis and confirm the existence of messenger RNA. They demonstrate that infection of Escherichia coli by phage T4 stops cell synthesis of host RNA and leads to T4 RNA synthesis. The T4 RNA attaches to cellular ribosomes and directs protein synthesis.

Charles Yanofsky and coworkers define the relationship between the order of mutatable sites in the gene coding for the Escherichia coli enzyme tryptophan synthetase and the corresponding amino acid replacements in the enzyme. It worked well for tyrptophan synthetase because the enzyme has two subunits, one of which could be mutated. The missense mutants in the alpha subunit could be mapped and related to the genetic fine structure of the gene. The property of correlating a mutation with an amino acid replacement is called colinearity.

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Yanofsky, C., B.C. Carlton, J.R. Guest, D.R. Helinski, and U. Henning. 1964. On the colinearity of gene structure and protein structure. Proc. Nat'l. Acad. Sci. 51:266-74 In Microbiology: A Centenary Perspective, edited by Wolfgang K. Joklik, ASM Press. 1999, p.392 [pdf]