Chapter 10 Control Circuits

Abstract

Lambda contains some forty genes organized into several operons. Although two of these operons are subject to classical repression, none of them can be understood entirely in these terms; it is now quite clear that positive controls play an essential role in the development of temperate phages. The general principles established by Jacob and Monod (1961) in their study of negative regulation were extended to positive regulation by Englesberg et al. (1965) in their study of the arabinose operon in Escherichia coli. An independent approach permitted at the same time the discovery of positive controls in temperate bacteriophages (see below).

After a description of the classical operon, this chapter will present new features of regulation in λ, notably positive and sequential control. Examples of complex circuits will then be briefly analyzed in terms of combinations of simple control operations. Finally, the necessary generalization of the concept of operon will be considered.

This chapter has no pretension of being complete in any respect (for instance, regulation at the translational level, which is no doubt quite important, will not be discussed because almost nothing is known about it in λ). It should serve as an introduction to the next three chapters, in which more facts will be considered in detail.

THE CLASSICAL OPERON
Jacob and Monod (1961) recognized the existence of groups of closely linked genes subject to coordinate regulation. They surmised that this coordinate regulation takes place at the transcriptional level, the genes in question being transcribed in linear sequence. This...