Lambda phage

About: Lambda phage is a research topic. Over the lifetime, 1609 publications have been published within this topic receiving 84675 citations. The topic is also known as: Enterobacteria phage lambda.

Evidence that ribosomal protein S10 participates in control of transcription termination

Abstract: We report the isolation of an Escherichia coli K-12 strain with a mutation, nusE71, that results in a change in ribosomal protein S10. Phage lambda fails to grow in hosts carrying the nusE71 mutation because the lambda N gene product is not active. The N product regulates phage gene expression by altering transcription complexes so that they can overcome termination barriers. This suggests that a ribosomal protein is involved in antitermination of transcription.

Dual role for Escherichia coli RecA protein in SOS mutagenesis.

Abstract: Induction of the Escherichia coli SOS system increases the ability of the cells to perform DNA repair and mutagenesis. Previous work has shown that this increased mutagenesis is the result of derepression of specific genes through a complex regulatory mechanism controlled by LexA and RecA proteins. One role of RecA protein in this process is to facilitate proteolytic cleavage of LexA protein (the repressor) in response to an inducing signal that reversibly activates RecA protein to perform this function. We show that activated RecA protein plays a second role in SOS mutagenesis, as revealed by analyzing repair of UV-damaged phage lambda in host mutants with alterations in the SOS regulatory system. First, phage mutagenesis was not expressed constitutively in a mutant that is derepressed through lack of functional LexA protein; activated RecA protein was still required. Second, phage mutagenesis was constitutively expressed in the presence of recA mutations that alter RecA protein so that it is activated in normally growing cells. There was also RecA-dependent constitutive expression of SOS mutagenesis in host mutants that lack functional LexA protein and carry plasmids. We discuss several possible biochemical mechanisms for this second role of activated RecA protein in SOS mutagenesis.

Development of a short-term, in vivo mutagenesis assay: the effects of methylation on the recovery of a lambda phage shuttle vector from transgenic mice

Abstract: Transgenic mice suitable for the in vivo assay of suspected mutagens at the chromosome level have been constructed by stable integration of a lambda phage shuttle vector. The shuttle vector, which contains a beta-galactosidase (beta-gal) target gene, can be rescued from genomic DNA with in vitro packaging extracts. Mutations in the target gene are detected by a change in lambda phage plaque color on indicator agar plates. Initial rescue efficiencies of less than 1 plaque forming unit (pfu)/100 micrograms of genomic DNA were too low for mutation analysis. We determined the cause of the low rescue efficiencies by examining primary fibroblast cultures prepared from fetuses of lambda transgenic animals. The rescue efficiency of 5-azacytidine-treated cells increased 50-fold over non-treated controls indicating that methylation was inhibiting rescue. The inhibitory role of methylation was supported by the observation that mcr deficient E. coli plating strains and mcr deficient lambda packaging extracts further improved lambda rescue efficiency. Present rescue efficiencies of greater than 2000 pfu/copy/micrograms of genomic DNA represent a 100,000-fold improvement over initial rescue efficiencies, permitting quantitative mutational analysis. The background mutagenesis rate was estimated at 1 x 10(-5) in two separate lineages. Following treatment with the mutagen N-ethyl-N-nitrosourea (EtNU), a dose dependent increase in the mutation rate was observed in DNA isolated from mouse spleen, with significant induction also observed in mouse testes DNA.