IGEM:Caltech/2007/Project/Cro: Difference between revisions
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===Potential Binding Combinations=== | ===Potential Binding Combinations=== | ||
When repressor binds to OR2 [only], RNA polymerase bind to PRM and prevents its binding to the PR region. leading to transcription of cI tenfold (Positive Control) and turning off the ''cro'' gene (Negative Control). | When cI repressor binds to OR2 [only], RNA polymerase bind to PRM and prevents its binding to the PR region. leading to transcription of cI tenfold (Positive Control) and turning off the ''cro'' gene (Negative Control). | ||
When repressor binds to OR1, RNA polymerase favors neither PRM nor PR. Polymerase access to PR is blocked, but the absence of repressor fails to attract polymerase to the PRM region, leading to a very low level of PRM. | When cI repressor binds to OR1, RNA polymerase favors neither PRM nor PR. Polymerase access to PR is blocked, but the absence of repressor fails to attract polymerase to the PRM region, leading to a very low level of PRM. | ||
A repressor bound to OR3 blocks PRM transcription, but polymerase can still easily reach PR. | A cI repressor bound to OR3 blocks PRM transcription, but polymerase can still easily reach PR. | ||
==Role in Lambda Lifecycle== | ==Role in Lambda Lifecycle== | ||
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The switch to lysis is brought on by stimuli [such as ultraviolet light] that damages the bacteria’s DNA. This activates a bacterial protein (RecA) which cleaves repressor molecules. As the concentration of cI drops, OR1 and OR2 become unoccupied. cI transcription ceases, and the RNA polymerase binds to PR to transcribe ''cro''. Cro binds independently to OR1, OR2, and OR3, preventing PRM transcription. The genes to the right of ''cro'' are also transcribed, which leads to the lytic phase. | The switch to lysis is brought on by stimuli [such as ultraviolet light] that damages the bacteria’s DNA. This activates a bacterial protein (RecA) which cleaves the cI repressor molecules. As the concentration of cI drops, OR1 and OR2 become unoccupied. cI transcription ceases, and the RNA polymerase binds to PR to transcribe ''cro''. Cro binds independently to OR1, OR2, and OR3, preventing PRM transcription. The genes to the right of ''cro'' are also transcribed, which leads to the lytic phase. | ||
As parts of a bistable switch, Cro and cI repressor protein levels in the cell directs the choice between lysis and lysogeny : | |||
- When no cI is present, the ""cro"" gene produces Cro (leading to lysis). | |||
- With higher cI repressor levels in the cell, only the cI gene is active, resulting in lysogeny. | |||
- At very high cI concentrations, both cI and cro transcription is repressed. | |||
==Original Goal== | ==Original Goal== |
Revision as of 08:28, 26 October 2007
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