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lecture 14--phages and genetics

lecture 14--phages and genetics - The dsDNA phages are...

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The dsDNA phages are larger and more sophisticated, but do the same job: specific recognition, genome insertion, expression/ replication, packaging, and escape.
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T4, a virulent phage, efficiently subverts the cell’s machinery.
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Gene expression is temporally regulated; T4 manipulates the host gene expression system
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A single T4 virion has a linear, dsDNA chromosome with over 250 genes. Replicating linear chromosomes requires some way of replicating ends. T4 solves this problem by making a “concatemer” of genomes, end to end. A “headful” packaging mechanism ensures that each virion gets >100% of a genome.
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For all the lytic phages, the end is not so good for the cell. But what is the point of a virus? a) kill cells b) make as many virus particles as possible c) make as many copies of the virus genome as possible.
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Lambda is a temperate phage--it can grow lytically or lysogenically. Lytic growth is what we’ve seen for other phages. Lysogenic growth maintains the phage DNA as a plasmid or as part of the cell’s chromosome.
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Upon entering the cell, linear lambda DNA circularizes, behaving like a plasmid. (This takes care of the replication problem.)
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The “decision” whether to undergo lytic growth or lysogeny is a problem of gene
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