Part:BBa_K566002
Biphasic switch
The biphasic switch combines positive and negative regulation through a single input. It is turned on by low lambda cI concentrations and off by high cI concentrations (1). There are two well-known sets of cI binding sites in lambda (OR and OL) spaced 2.4 kb apart and composed of three operators each (OR1:OR2:OR3; OL1:OL2:OL3) (2). cI has a higher affinity for OR1 and OR2 operators, where binding positively regulates the pRM promoter. In presence of the OL set, cI octamerise specifically binding to the two sets of operators (OR and OL) at the same time and therefore forming a DNA loop (3). Such structure stabilizes cI's binding to OR3, allowing pRM's repression at cI high concentrations.
Usage and Biology
The biphasic switch may be used to control both expression and repression of pRM through a single input, which must control cI protein concentration. If repressor cI434 is placed under pRM's control along with the gene of interest, this switch may be coupled with the modified promoter pRM434 (which is stimulated by cI but repressed by cI434,BBa_I12006) to form a two-state switch. The expected behavior will be that at low concentrations of cI, both promoters will be activated. However, because of cI434 repressing pRM434, only pRM will stay on eventually leading to the first state. At high concentrations of cI, pRM -and consequently cI434- will be turned off, allowing pRM434 to be activated by cI and leading to a second state. pRM promoter from Phage 434 (not to confuse with pRM434 mentioned above) seems to exhibit the same biphasic behavior 4.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21INCOMPATIBLE WITH RFC[21]Illegal BglII site found at 95
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000COMPATIBLE WITH RFC[1000]
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