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EM of a mating between Hfr and F- strains of E. coli |
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The course focuses on mechanisms of gene regulation as the means for demonstrating the uses of genetics in investigating biological systems. The first topic is the lactose operon of Escherichia coli. Brief summaries of the system can be found in in Principles of Genetics, 3rd Edition by Snustad and Simmons, p. 573-584, in Genes VII by Lewin, p. 275-298, and in Molecular Biology by Weaver, p. 183-198. Useful review articles can be found in The Operon, edited by Miller and Reznikoff, in particular, the chapter by Beckwith, "lac: The Genetic System", p. 11, and the chapter by Reznikoff, "The lac Promoter", p. 221. Introduction to the lac operon: physiology and early genetics. Lecture by Dr. Wolf with provided handouts. The "PaJaMo" experiment from which the concept of negative control of gene expression was derived. Pardee, Jacob, and Monod, J. Mol. Biol. 1:165, 1959. Pay particular attention to Fig. 3 and Fig. 4 and to the descriptive phrases used in the Discussion; note how repressor control is proposed as the universal genetic mechanism. Dr. Wolf will do this paper as an example. The Operon Model. Jacob et al., Compte Rendus 250:1727, 1960; English translation published in Papers in Bacterial Genetics, edited by G. Stent, p. 395. Pay particular attention to the way in which partial diploids are used to distinguish genes from regulatory sites. How do the diploids in this paper differ from those in the previous paper? Isolation of lac promoter mutants. Scaife and Beckwith, Cold Spring Harbor Symp. Quant. Biol. 31:403, 1966. Concentrate on the genetic selection and the properties of the mutants. If you do not know what nonsense suppressors are, look them up in your genetics text book. What is polarity and how do the effects of suppressors distinguish promoter mutants from nonsense mutants? Isolation of phi 80dlac transducing phages, an early example of genetic engineering. Beckwith, Signer, and Epstein, Cold Spring Harbor Symp. Quant. Biol. 31:393, 1966. You need read only p. 393-396. Concentrate on understanding how the transposition strains were made and the steps leading to formation of the lac specialized transducing phages. Be sure you can draw out the integration of the episome into the chromosome. Consider the potential uses of the phage and thus why this paper is a landmark. You should review in a genetics textbook (e.g., Snustad and Simmons, p. 431-434) the process of specialized transduction with phage lambda, which is similar to that of phage phi 80. Deletion mapping of promoter mutants. Ippen et al., Nature 217:825, 1968. Diagram each cross in Table 2 and try to explain what was selected and what was scored. Note that "homogenotization" refers to the process of forming a diploid strain in which a given allele is present on both gene copies; in the cases here, it depends on the fact that the cells contain two or more copies of both the chromosome and the episome. (Continued on page 2) |
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