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 vivo gene delivery and expression by bacteriophage lambda vectors

Abstract: Aims: Bacteriophage vectors have potential as gene transfer and vaccine delivery vectors because of their low cost, safety and physical stability. However, little is known concerning phage-mediated gene transfer in mammalian hosts. We therefore performed experiments to examine phage-mediated gene transfer in vivo. Methods and Results: Mice were inoculated with recombinant lambda phage containing a mammalian expression cassette encoding firefly luciferase (luc). Efficient, dose-dependent in vivo luc expression was detected, which peaked within 24 h of delivery and declined to undetectable levels within a week. Display of an integrin-binding peptide increased cellular internalization of phage in vitro and enhanced phage-mediated gene transfer in vivo. Finally, in vivo depletion of phagocytic cells using clodronate liposomes had only a minor effect on the efficiency of phage-mediated gene transfer. Conclusions: Unmodified lambda phage particles are capable of transducing mammalian cells in vivo, and may be taken up – at least in part – by nonphagocytic mechanisms. Surface modifications that enhance phage uptake result in more efficient in vivo gene transfer. Significance and Impact of the Study: These experiments shed light on the mechanisms involved in phage-mediated gene transfer in vivo, and suggest new approaches that may enhance the efficiency of this process.

Phage Lambda’s Accessory Genes

Abstract: INTRODUCTION Phage λ contains some 50 kbp of DNA, and approximately 50 genes have been revealed by analysis of mutants and phage proteins. Most of these genes are essential for perpetuation of the virus in either the lytic or the lysogenic mode of growth. For example, 27 genes are required for the phage to produce mature progeny and form plaques. Five other genes are required for repression, integration, and excision. Several other genes, which form the subject of this paper, are not absolutely required for either lysis or lysogeny. These genes are distributed in several places along the λ genome, and the regions carrying them can be deleted with minimal effects on phage development. Because they are not essential for “normal” phage development in standard hosts and under standard laboratory conditions these genes have been collectively designated as nonessential or dispensable. However, it is becoming clear that these genes are not functionless but, rather, they often have interesting and even essential roles in certain circumstances. Consequently, we prefer to call them accessory genes. In this paper, we review λ ’s accessory genes and discuss their role with respect to both λ and Escherichia coli . Since these genes are dispensable for “normal” λ development, they have not been studied extensively, and our understanding of their expression and function is limited. Nevertheless, we can make a few general statements about their roles. Some appear to be nonessential for phage growth because an analogous or compensating function exists in the host. Others are essential...

Genetic analysis of Escherichia coli integration host factor interactions with its bacteriophage lambda H' recognition site.

Abstract: The bacteriophage P22-based challenge phage system was used to study the binding of integration host factor (IHF) to its H' recognition site in the attP region of bacteriophage lambda. We constructed challenge phages that carried H' inserts in both orientations within the P22 Pant promoter, which is required for antirepressor synthesis. We found that IHF repressed expression of Pant from either challenge phage when expressed from an inducible Ptac promoter on a plasmid vector. Mutants containing changes in the H' inserts that decrease or eliminate IHF binding were isolated by selecting challenge phages that could synthesize antirepressor in the presence of IHF. Sequence analysis of 31 mutants showed that most changes were base pair substitutions within the H' insert. Approximately one-half of the mutants contained substitutions that changed base pairs that are part of the IHF consensus binding site; mutants were isolated that contained substitutions at six of the nine base pairs of the consensus site. Other mutants contained changes at base pairs between the two subdeterminants of the H' site, at positions that are not specified in the consensus sequence, and in the dA + dT-rich region that flanks the consensus region of the site. Taken together, these results show that single-base-pair changes at positions outside of the proposed consensus bases can weaken or drastically disrupt IHF binding to the mutated site.

An ancient player unmasked: T4 rI encodes a t-specific antiholin.

Abstract: Phage T4 effects lysis by its holin T and its endolysin E. Lysis is inhibited (LIN) if the infected cell is subjected to secondary infections by T4 phage particles. The T4 rI gene is required for LIN in all hosts tested. Here, we show that a cloned rI gene can impose a T-specific LIN on T-mediated lysis in the context of the phage lambda infective cycle, in the absence of other T4 genes and without secondary infection by T4. Moreover, it is shown that the T holin accumulates in the membrane during LIN, forming SDS-resistant oligomers. We show by cross-linking experiments that a T-RI heterodimer is formed during LIN, demonstrating that RI belongs to the functional class of antiholins, such as the S107 protein of lambda, which heterodimerizes with its cognate holin, S105. Finally, we show that the addition of Ni(2+) ions to the medium can block lysis by a T protein hexahistidine-tagged at its C-terminus, suggesting that liganding of the periplasmic domain is sufficient to impose lysis inhibition. The results are discussed in terms of a model in which the LIN-inducing signal of the secondary infecting phage influences a conformational equilibrium assumed by RI in the periplasm.