Phage lambda: Difference between revisions
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== Life Cycle == | == Life Cycle == | ||
=== Lytic Cycle === | === Lytic Cycle === | ||
The lytic cycle | The lytic cycle produces progeny phage particles and results in the death of the host bacteria. | ||
==== Adsorbtion and Injection ==== | ==== Adsorbtion and Injection ==== | ||
Revision as of 19:43, 8 August 2011
Bacteriophage λ is the archetype of the lambdoid, or lambda-like phage, a subclass of the siphoviridae. λ is a temperate phage; it can grow either lytically or lysogenically. The λ strain used most often in labs, although called wt, is λPaPa, named after the parental strains from Pasedena California and the Institut Pasteur in Paris. [1]
Morphology
The λ phage has an icosahedral head about 50 nm in diameter, and a flexible, noncontractile tail about 150nm long.[2][1] The head is formed from the proteins E, D, B, W, FII, B*, X1, and X2. [3] The head is the capsid, and contains a single double-stranded DNA molecule about 48 kb in length; by weight the genome is about 32x106 Da and comprises about half of the phage's weight.[2] The DNA is linear when packaged, and recircularizes using host ligase at the cos (cohesive end site) once injected into the host.[2] [3] The wt λ does not have tail fibers, although these may be present on certain strains.[1]
Genome Organization
Life Cycle
Lytic Cycle
The lytic cycle produces progeny phage particles and results in the death of the host bacteria.
Adsorbtion and Injection
The tip of the phage tail (J protein) attaches to the host cell protein lamB, which is displayed on the outer membrane.[2] The dsDNA is injected through the tail as a linear genome, when the phage tail interacts with the inner membrane protein ptsM and recircularizes once inside the host due to complementary 12nt long sticky ends. [2]
Early Gene Expression
The cro gene produces an immediate-early gene product.[4] CII and CIII are delayed-early gene products. [4]
Middle Gene Expression
DNA Replication
Replication directly after injection proceeds via θ (theta) replication after host gyrase supercoils the λ DNA. [3] Replication proceeds via rolling circle replication when entering the lytic cycle, aided by phage-encoded endonuclease which cuts the (+) strand.[3]
Late Gene Expression
Packaging
The DNA replicated by rolling circle remains as concatomers until terminase cleaves the cos site and one end of the DNA is packed into the capsid.[3] Proteins B, C, and Nu3 form the capsid precursors, which are aided by host groEL and groES to combine with E to form an immature capsid. [3] The proteins E and C combined and are reformed into X1 and X2, which make a mature capsid once B* is added (from B) and Nu3 is degraded. [3]
D protein is added to the capsid and standardizes the size of the head , then the λ DNA is inserted until the terminase cuts the DNA at the next cos site and W and FII proteins stabilize the capsid.[5] [3]
Tails are formed seperately from the far end of the structure in the proteins in the order J, I, L, K, H, G, M, V, U, H, and Z and attach spontaneously to mature capsids by proteins W and FII.[3]
Lysis
Proteins R and S are used to degrade the bacterial membranes, with S acting on the inner and R on the outer membrane. [3] About 100 phage are released per host, and infection to release takes about 35 minutes. [3]
Lysogenic State
The lysogenic lifecycle is the result of integration of the λ DNA into the host genome, and does not result in the death of the host cell. The λ DNA/host DNA unit is termed a prophage, and decendants of the prophage are capable of producing phage when the λ DNA excises from the host DNA. [6] The λ DNA is integrated at the attP (for attachment phage) and the attB (for attachment bacteria) loci.[4]
Lysis-Lysogeny Switch
Prophage Induction
See also
- Lambda Gene List
- Enterobacteriophage lambda at the NCBI taxonomy browser
- wikipedia: Lambda_phage
- ICTVdb entry
- Siphoviridae at MicrobeWiki
- Phage lambda on UniProt
References
See Help:References for how to manage references in EcoliWiki.
- ↑ 1.0 1.1 1.2 Hendrix, RW & Duda, RL (1992) Bacteriophage lambda PaPa: not the mother of all lambda phages. Science 258 1145-8 PubMed
- ↑ 2.0 2.1 2.2 2.3 2.4 Edited by Roger W. Hendrix, Jeffrey W. Roberts, Franklin W. Stahl and Robert A. Weisberg (1983) Lambda II (Cold Spring Harbor Laboratory, Cold Spring Harbor, NY)
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Edward K. Wagner et al (2007) Basic Virology (Wiley-Blackwell) ISBN 978-1-4051-4715-6
- ↑ 4.0 4.1 4.2 Bruce A. Voles (2002) The Biology of Viruses (McGraw-Hill, Boston) ISBN 0-07-237031-9
- ↑ Neidhardt, FC et al. (1996) Escherichia coli and Salmonella typhimurium: Cellular and Molecular Biology 2nd ed. (ASM Press, Washington, DC)
- ↑ Appleyard, RK (1954) Segregation of Lambda Lysogenicity during Bacterial Recombination in Escherichia Coli K12. Genetics 39 429-39 PubMed