Chapter 12 Regulation of Repressor Synthesis

Abstract

Repressors of gene action in bacteria are assumed to be synthesized continuously, the genes under their control being expressed when the repressor is inactivated. This is known to be true for the lac repressor, which is reversibly inactivated by specific inducers (Gilbert and Müller-Hill, 1966). Such control seems reasonable in operons such as lac where it is advantageous to the bacterium to be able to respond as quickly as possible to environmental change. In temperate bacteriophages, however, induction of the prophage is usually irreversible, leading to productive growth of the phage and lysis of the bacteria. Thus one might expect that phage repressors need not be synthesized during all phases of the growth cycle. There is now evidence supporting the idea that repressor synthesis is regulated in λ.

REGULATION OF GENE cI
Only two genes are known to be expressed by the λ prophage: cI, the repressor gene, and rex, whose product prevents the growth of rII mutants of phage T4 (Howard, 1967). Conditions have been found in which the genes cI and rex stop functioning more or less permanently in lysogens. This can be seen in the behavior of cells lysogenic for the temperature-sensitive prophage λc1857 containing mutations in gene N and in either gene O or P (Eisen et al., 1968a; and Calef and Neubauer, 1968). When such a lysogen is heated, immunity and, more slowly, rex function are abolished. When these lysogens are grown for prolonged periods at high temperature and are then allowed to grow at...