Lecture 13 viruses

Lecture 13 viruses - The heat-shock response is an example...

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Unformatted text preview: The heat-shock response is an example of regulating gene expression at the level of protein stability; it is also an example of positive feedback. Under normal conditions, there is a small amount of proteases such as DnaK in the cell. DnaK has a high afFnity for two things: denatured protein, and sigmaH. The sigmaH gene has a weak sigma 70 promoter; whatever sigma H is produced is degraded. A “heat shock” denatures proteins. All the cell’s DnaK is distracted by denatured protein. The small amount of sigmaH that is produced is allowed to survive. RNAP (sigmaH) transcribes the heat- shock regulon--including dnaK and rpoH . How does it all end? Some plasmids do not encode anything remotely useful. A B How do they avoid getting voted off the island? One solution: Replicate faster than the chromosome. Another system: Threaten to kill the cell if not replicated and present in each daughter. Weaver 2007 GUG GUG GUG An “addiction module” is a very selfsh genetic system. Another strategy: Replicate and spread from cell to cell. F factor is a plasmid encoding replication and transfer ( tra ) proteins; it spreads through an F-encoded pilus Another strategy: Spread from cell to cell. Viruses (phages) are essentially selfsh DNA that has learned how to spread From genome to genome without direct contact. Filamentous ssDNA viruses act like conjugative plasmids out of control. ssDNA enters the cell; cell machinery makes the ssDNA into dsDNA. This serves as a template for expressing viral proteins, and for making more ssDNA.ssDNA....
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This note was uploaded on 04/05/2011 for the course MIC 102 taught by Professor Appleman during the Fall '08 term at UC Davis.

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Lecture 13 viruses - The heat-shock response is an example...

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