Prophage Repression as a Model for the Study of Gene Regulation I. Titration of the λ Repressor

Open Access
Publisher Website
Google Scholar
Abstract
Wiesmeyer, Herbert (Vanderbilt University, Nashville, Tenn.). Prophage repression as a model for the study of gene regulation. I. Titration of the λ repressor. J. Bacteriol. 91: 89–94. 1966.—The concentration of λ repressor molecules within a λ lysogenic cell was estimated from the multiplicity of superinfecting homologous phage necessary to permit replication and release of plaque-forming units. A multiplicity of 20 superinfecting phage was found sufficient to permit replication to occur in the normal λ lysogen. The phage released after lysis of the superinfected lysogen was composed of both prophage and superinfecting phage types. Superinfection of the lysogen at lower multiplicities resulted in the lysis of only a small percentage of infected cells and is thought to represent a possible heterogeneity of repressor concentration in the lysogenic population. Viability of the superinfecting particle was found to be unnecessary for titration of the repressor. The repressor concentration in three lysogens of the nonultraviolet-inducible mutant of λ, λ ind− , was found to be greater than 20 regardless of the host bacterium. However, the number of cells yielding phage after superinfection was found to vary with the particular host. The specificity of the λ repressor was shown to be limited to homologous phage, as determined following heterologous superinfection experiments with phages T6r, 82c, 434c, 434hy, and 424. In all instances except that of superinfection with phage 434hy, only heterologous phage replication occurred. Superinfection by phage 434hy resulted in the release of both prophage and superinfecting phage types. The latter type represented approximately 80% of the total phage released.