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.

In situ detection of sequence-specific DNA binding activity specified by a recombinant bacteriophage.

Abstract: We have used a recombinant bacteriophage that expresses the DNA-binding domain of C/EBP to optimize conditions for a screening technique that may facilitate the cloning of genes that encode sequence-specific DNA-binding proteins. The method relies on the expression of cDNA inserts in bacteriophage lambda gt11. Fusion protein adsorbed onto nitrocellulose filters is probed with radioactive, double-stranded DNA as a ligand. Two procedures greatly increase the level of binding between ligand and recombinant fusion protein. First, nitrocellulose filters are processed through a denaturation/renaturation regimen using 6 M guanidine hydrochloride. Second, synthetic DNA corresponding to the specific binding site is catenated extensively using DNA ligase. The combination of these procedures leads to remarkably strong detection signals. Specific DNA-binding signals can be detected on duplicate filters, and filters can be washed and reused by repeating the cycle of denaturation/renaturation.

Isolation of the Bacteriophage Lambda Receptor from Escherichia coli

Abstract: A factor which inactivates the phage lambda can be extracted from Escherichia coli. This factor is a protein and is located in the outer membrane of the bacterial envelope. It is found in extracts of strains which are sensitive to phage lambda, but not in extracts of strains specifically resistant to this phage. We conclude that this factor is the lambda receptor, responsible for the specific adsorption of the phage lambda to E. coli cells. A partial purification of the lambda receptor is described. Inactivation of the phage by purified receptor is shown to be accompanied by the release of deoxyribonucleic acid from the phage.

Repeatability and Contingency in the Evolution of a Key Innovation in Phage Lambda

Abstract: The processes responsible for the evolution of key innovations, whereby lineages acquire qualitatively new functions that expand their ecological opportunities, remain poorly understood. We examined how a virus, bacteriophage λ, evolved to infect its host, Escherichia coli, through a novel pathway. Natural selection promoted the fixation of mutations in the virus’s host-recognition protein, J, that improved fitness on the original receptor, LamB, and set the stage for other mutations that allowed infection through a new receptor, OmpF. These viral mutations arose after the host evolved reduced expression of LamB, whereas certain other host mutations prevented the phage from evolving the new function. This study shows the complex interplay between genomic processes and ecological conditions that favor the emergence of evolutionary innovations.

Molecular characterization of human immunodeficiency virus type 1 cloned directly from uncultured human brain tissue: identification of replication-competent and -defective viral genomes.

Abstract: All presently available replication-competent proviral clones of human immunodeficiency virus type 1 (HIV-1) are derived from cell culture-amplified virus. Since tissue culture is highly selective for viral strains with an in vitro growth advantage, such clones may not be representative of the biologically relevant virus present in vivo. In this study, we report the molecular cloning and genotypic characterization of 10 HIV-1 genomes directly from uncultured brain tissue of a patient with AIDS dementia complex. Targeting unintegrated circular HIV-1 molecules for recombinant lambda phage cloning, we obtained four full-length genomes with one or two long terminal repeats (LTRs), three defective genomes with internal deletions, two rearranged genomes with inverted LTR sequences, and one integrated proviral half with flanking cellular sequences. Nucleotide sequence analysis of these clones demonstrated chromosomal integration, circle formation, genomic inversion, and LTR-mediated autointegration of HIV-1 genomes in vivo. Comparison of a 510-bp hypervariable envelope region among 8 lambda phage-derived and 12 polymerase chain reaction-derived clones from the same brain specimen identified a predominant viral form as well as genetically divergent variants. Variability among 19 of 20 clones ranged between 0.2 and 1.2%. One clone exhibited 8.2% nucleotide sequence differences consisting almost exclusively of G-to-A changes. Transfection of the four full-length HIV-1 genomes identified one clone (YU-2) as replication competent and exhibiting growth characteristics similar to those of tissue culture-derived macrophage tropic strains of HIV-1. These results demonstrate, for the first time, that replication-competent HIV-1 genomes, complex mixtures of defective viral forms, and chromosomally integrated provirus persist in vivo. In addition, the brain-derived viral clones are expected to prove valuable for future studies of macrophage and neurotropism as well as for the analysis of other viral properties that are subject to in vitro selection pressures.