What are plaques in phages?

What are plaques in phages?

A phage plaque is a clearing in a bacterial lawn. Plaques form via an outward diffusion of phage virions that is fed by bacterial infection. Anything that slows phage diffusion can impede plaque development and thereby plaque size.

How are phage plaques formed?

If a phage lysogenized a host cell immediately upon infection, it would never form a plaque. Instead, when temperate phage infects a population of exponentially growing cells, each phage produces a plaque with a “bulls-eye” plaque morphology, a turbid center surrounded by a ring of clearing.

What is the function of CRO protein?

In a purified transcription system, the Cro protein is an effective and specific repressor of RNA synthesis from the N and cro genes; thus Cro is an autorepressor which regulates its own synthesis.

Is burst size positively or negatively correlated with plaque size?

It is reasoned that the more time the phage progeny spends inside the host, the less time it would be able to diffuse to a new host. It is also intuitively apparent that a larger burst size would result in a larger plaque size.

What is the purpose of plaque assay?

The plaque assay is a well established method for measuring virus concentration as it relates to infectious dose. The assay relies on determining the number of plaque forming units (pfu) created in a monolayer of virus-infected cells.

Is lambda Cro a transcription factor?

Bacteriophage lambda encodes two repressors: the Cro repressor that acts to turn off early gene transcription during the lytic cycle, and the lambda or cI repressor required to maintain lysogenic growth….Cro repressor family.

How does Cro bind to DNA?

The cro protein binds to the same three sites in the right operator (OR) of bacteriophage lambda DNA as does the lambda repressor. Dimethyl sulfate protection experiments reveal major groove contacts for both proteins, and cro protein protects from methylation a subset of those purines protected by lambda repressor.

What do plaque forming units determine?

Plaque forming units (PFU) are a measure of the quantity of viruses that are capable of lysing host cells and forming a plaque.

What does high PFU mean?

A high particle-to-pfu ratio is sometimes caused by the presence of noninfectious particles with genomes that harbor lethal mutations or that have been damaged during growth or purification.

How do you calculate plaque titre?

To determine the virus titer, the plaques are counted. To minimize error, only plates containing between 10 and 100 plaques are counted, depending on the size of the cell culture plate that is used. Statistical principles dictate that when 100 plaques are counted, the sample titer will vary by plus or minus 10%.

What causes unstable plaque?

The unstable atheroma. Plaque rupture occurs when the mechanical stresses in the fibrous cap exceed a critical level that the tissue can withstand. Several factors increase stress in the atheroma. A thin, fibrous cap overlying a large lipid pool causes very high stresses in the fibrous cap.

What kind of transcription factor is lambda Cro?

The lambda Cro repressor binds to DNA as a highly flexible dimer. The crystal structure of the lambda Cro repressor reveals a HTH DNA-binding protein with an alpha/beta fold that differs from other Cro family members, possibly by an evolutionary fold change….Cro repressor family.

What is the lambda repressor?

The lambda repressor is a self assembling dimer also known as the cI protein. It binds DNA in the helix-turn-helix binding motif. It regulates the transcription of the cI protein and the Cro protein. The life cycle of lambda phages is controlled by cI and Cro proteins.

What does lambda phage stand for?

Find sources: “Lambda phage” – news · newspapers · books · scholar · JSTOR (January 2012) Enterobacteria phage λ (lambda phage, coliphage λ, officially Escherichia virus Lambda) is a bacterial virus, or bacteriophage, that infects the bacterial species Escherichia coli (E. coli).

How are lambda phage libraries used to amplify DNA?

Similarly, a lambda phage library can be applied to a bacterial lawn, which then develops plaques, each containing the recombinant DNA from only one phage particle. The blotting procedure then identifies the plaques that are cultured to amplify the target DNA.

What is the pathophysiology of bacterial phage lambda?

Bacteriophage lambda is a virus that infects E. coli. The typical infection cycle results in the lysis of the E. coli cell and the release of about 100 progeny phage particles, each capable of infecting another cell.

What are the nonessential lambda phage genes?

Several nonessential lambda phage genes include lysogenic conversion genes, like bor and lom that are involved in host interactions, and exo, bet, and gam that aid in recombination events. Other exclusion genes such as rex and sie prevent further infections by phages. Resumption of the lytic phase is preceded by assembly of virions.