Repressor and rex product of coliphage lambda: lack of collaboration and joint controls.

Abstract

Exposure to 41° C for 10 to 100 minutes rapidly inactivates λ repressor bearing several ts mutations in the A or B region of gene cI, but does not result in simultaneous rapid loss of the rex function, which restricts phage T4 rII. One may conclude that the rex product does not directly collaborate with the repressor protein. Immediate loss of the rex activity at 47.5° C, observed with most of the λ cIts mutants and even λ cI+, appears to be unrelated to the repressor inactivation. In tof+ lysogens carrying nonlethal cIts prophage mutants, the prolongation of induction at 41° C ultimately results in irreversible loss of the rex function, but only after about six cell generations. In similar experiments with tof deficient lysogens, loss of the rex activity requires about eleven cell generations and the rex function is regained in less than 30 minutes after return of the lysogen to 30° C. Two methods of rex assay, the more sensitive “phage yield method” and the “infective center method”, were employed.