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.

Phage lambda's generalized recombination system. Study of the intracellular DNA pool during lytic infection.

Abstract: A phage DNA transfection assay is described that permits the measurement of frequencies of recombinant DNA molecules. This method was used to investigate the time course of action of the phage-specified generalized recombination system, the Red system, during lytic infection. Two observations of interest have emerged from this study: 1. There is a distinct lag before significant numbers of recombinant molecules are detected. 2. The presence of an active recB gene product in host cells produces an early shut-off of recombination.

In Vivo Methylation of Bacteriophage φX174 DNA

Abstract: A mutant (designated mec(-)) has been isolated from Escherichia coli C which has lost DNA-cytosine methylase activity and the ability to protect phage lambda against in vivo restriction by the RII endonuclease. This situation is analogous to that observed with an E. coli K-12 mec(-) mutant; thus, the E. coli C methylase appears to have overlapping sequence specificity with the K-12 and RII enzymes; (the latter methylases have been shown previously to recognize the same sequence). Covalently closed, supertwisted double-standed DNA (RFI) was isolated from C mec(+) and C mec(-) cells infected with bacteriophage phiX174. phiX. mec(-) RFI is sensitive to in vitro cleavage by R.EcoRII and is cut twice to produce two fragments of almost equal size. In contrast, phiX.mec(+) RFI is relatively resistant to in vitro cleavage by R.EcoRII. R.BstI, which cleaves mec(+)/RII sites independent of the presence or absence of 5-methylcytosine, cleaves both forms of the RFI and produces two fragments similar in size to those observed with R. EcoRII. These results demonstrate that phiX.mec(+) RFI is methylated in vivo by the host mec(+) enzyme and that this methylation protects the DNA against cleavage by R.EcoRII. This is consistent with the known location of two mec(+)/ RII sequences (viz., [Formula: see text]) on the phiX174 map. Mature singlestranded virion DNA was isolated from phiX174 propagated in C mec(+) or C mec(-) in the presence of l-[methyl-(3)H]methionine. Paper chromatographic analyses of acid hydrolysates revealed that phiX.mec(+) DNA had a 10-fold-higher ratio of [(3)H]5-methylcytosine to [(3)H]cytosine compared to phiX.mec(-). Since phiX.mec(+) contains, on the average, approximately 1 5-methylcytosine residue per viral DNA, we conclude that methylation of phiX174 is mediated by the host mec(+) enzyme only. These results are not consistent with the conclusions of previous reports that phiX174 methylation is mediated by a phage-induced enzyme and that methylation is essential for normal phage development.

Analysis of mutations in the ninR region of bacteriophage lambda that bypass a requirement for lambda N antitermination.

Abstract: Two mutations in the ninR region of bacteriophage lambda that bypass a requirement for antitermination have been studied. One mutation, byp, has been cloned and mapped by marker rescue to a 417-base-pair segment in the ninR region of the genome. Analysis of the byp mutation by using promoter detection vectors, DNA sequencing, and S1 nuclease analysis showed that the byp mutation created a new promoter that transcribed gene Q. The second mutation analyzed was the deletion nin3. Sequence analysis revealed that 2,485 base pairs of the ninR region were removed, beginning within the ren gene and ending in an open reading frame termed ninG. The tR2 and tR3 terminators, and probably others, were removed by the nin3 deletion, thereby allowing the phage to be N independent and to grow in hosts defective for Nus antitermination factors. Images