"Another biologically even more interesting phenomenon was there to be analyzed, this one with the help of Tetsuo Iino, a graduate student from Japan. The issue here is a phenomenon called phase variation. This has to do with there being two different antigenic phases of Salmonella bacteria in the flagella. JL gives an example of this phenomenon. In the mosaic descriptions of different Salmonella strains, JL notes, you write down the somatic antigen of each of the two alternative phases that go along with it, which are interconvertible, in that a cell flips from being what is called specific phage into so called group phase, and vise versa. But it always alternates between the same two alternatives, thus you cannot predict what the second phase is going to be from what the first phase was. You can predict what the second phase is going to be, but only if you know the history of that particular strain."
"So what it looked like was two alternative states that the bacterium could be in and that the genetic potentiality was there for either or both, but that at any given moment it was expressing either one of the other. JL wanted to correlate that at a genetic level and see what he could find out about mechanism. He was able to do that and establish that there are two separate genes, one for the specific phase allele and one for the group phase allele. Thus if you start out with an I, you could, using different Salmonella strains, alter that to be a, b, c, d, e, f, g - any of the alternatives depending on the donor. He discusses some possible variations. You now have established two different genes - one controlling the specificity of the flagella when it is in the group state, and the other establishing the specificity of the flagella when it is in the non - specific state. JL ended up showing that there was an alternation of states that later on were then shown to be a DNA inversion. Mel Simon, JL notes, gets the most credit for a detailed examination of that phenomenon. So there is a specific enzyme that looks for certain sequences in the flanks of this DNA segment, and is able to cut the DNA and let it reseal in the opposite sense. This can go in one direction - and back again, back again, back again. This is what happens once every thousand divisions, and it is a way in which the bacteria can randomize what they expose to the outside world. They are not stuck with one overcoat, and if antibodies start developing against that overcoat they can go to the alternative one."
However, the observation and explanation of alternations in microbial states lacks any connection to the biochemistry required in molecular genetics. Compare the following explanation provided by Bruce Stocker, which is a true example of Molecular Genetics. Here, one of Joshua Lederberg's false claims to be a founder of Molecular Genetics is carefully obscured by the words "... later on were then shown to be a DNA inversion." . Thus Joshua Lederberg was NOT involved in this aspect of Molecular Genetics.
The 1998 University of Wisconsin "Oral History" Interview may be
found at
Joshua Lederberg's National Library of Medicine (NLM) site:
http://profiles.NLM.NIH.gov/BB/.
Search for the document with ID# bbbdhf.
Click here to see Bruce Stocker's explanation
While Joshua Lederberg can hardly have a claim to have worked in
Molecular Genetics (as opposed to Microbial Genetics), Esther
M. Zimmer Lederberg published work with colleague Bruce A. D.
Stocker that did involve Molecular Genetics:
Lederberg, E. M., Stocker, B. A. D., 1970, "Phase variation in
rec– mutants of Salmonella typhimurium",
Bacteriological Proceedings p. 35 (abstract)