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lac: The Genetic System

Jonathan R. Beckwith


This chapter deals with the methods and tools used for genetic analysis of the lac1 operon. The specific problems which arise in the genetic analysis of this system are, in many cases, similar to those encountered in other genetic regulatory units. Therefore, the solutions to these problems can provide a methodology applicable to at least certain of these other systems. The generality of the techniques and approach will be evaluated in this chapter. A more direct application of these techniques derives from the existence of strains in which the lac genes are fused to other bacterial operons, such as the trp and purE operons (Beckwith et al. 1966; Jacob et al. 1965). Since, in such strains, the lac genes are now part of the other operon, nearly all the methodology used for analysis of lac can be used for that operon (see Bassford et al., this volume).

Most of the major concepts of operon structure, expression, and regulation have come out of the work on the lac operon of Escherichia coli. That lac has generated so many of these ideas is due to several factors: (1) The happy coincidence of Monod and Jacob working in the same institute, thus affording a collaboration between two creative minds in the fields of bacterial physiology and regulation and bacterial genetics. The interplay of these fields has been of obvious importance to the rapid progress in understanding the mechanisms of genetic control. (2) The intuition of Monod, Jacob, and coworkers in formulating...

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