Lysogenization by Lambda Lacking Repressor and N Function

Abstract

This report concerns lysogenization by λ phages mutated in gene N. The product of this essential gene greatly enhances the transcription of the genes concerned with the integration of λ as a prophage, and of the genes required for replication of λ DNA (Kourilsky et al., 1968, Kumar et al., 1969, Nijkamp et al., 1970). Nsus mutants infecting a nonpermissive (pm⁻) host can replicate in the bacterial cytoplasm, due to limited expression of λ genes O and P (Signer, 1969). Bacteria infected with λNsus (two or more infecting particles per bacterium) produce carrier clones in which most of the bacteria contain 30–50 λ plasmids (Lieb, 1970). Even λ genomes containing two mutations in N, or an N deletion (Matsubara and Kaiser, 1968), replicate as plasmids, so that N product is not required for limited replication of λ.

N mutants lysogenize poorly, but stable lysogens can be obtained (Brooks, 1965). Signer (1969 Signer (1970) concluded that N function is required for λ integration, and that lysogenization by phages with a single mutation in N is due to “leaky” N function. In this paper I will present data confirming a previous report that phages with two mutations in N (nonleaky mutants) can lysogenize without the help of N⁺ phage (Cross and Lieb, 1967).

After a λ genome has been integrated into the bacterial chromosome, its transcription is repressed by the product of gene cI. Inactivation of the cI product generally results in excision and replication of the prophage, terminating in the...