Induction of lambdoid prophages by amino acid deprivation: Differential inducibility; Role of recA

Summary

Lambda prophage in auxotrophic lysogens can be induced by omission of one or combinations of the required amino acids from the culture medium. Such amino acid deprivation can result in nearly as effective induction of lambda as thymine deprivation. Prophage 424 is also induced equally effectively under both conditions although to a lesser extent than lambda. By contrast prophage 21 and λi²¹ are differentially induced effectively by thymine deprivation and virtually not at all during amino acid deprivation. The same differential induction of 21 and equivalent induction of λ and 424 occur when all three prophages are present in the same lysogen. Increasing the levels of λ repressor with a cI carrying-plasmid prevented amino acidless induction of λ as did the λind ⁻ mutation. A recA, but not a recB, mutation in the host prevented induction by amino acid deprivation. A recC mutant host showed increased spontaneous induction of λ and 21 prophages. The findings reported are used as an argument that the recA protease probably is not itself acting as the inducing protease and that a likely source of the observed specificity is an effector molecule. Different effector molecules may be produced in response to different exigent situations, to which the phage repressors may have evolved sensitivity. λi⁸⁰ was inducible both by amino acid and thymine deprivation.