We can subdivide our clock into two parts: the activator module and the repressor module. The activator module consists of the constitutive promoter driving the NifA gene, thereby producing a constant amount of NifA. We will be using three different BioBrick promoters - corresponding to low, medium, and high outputs of NifA respectively. The NifA protein binds to the nifHp promoter of the repressor module, activating transcription of the NifL gene. Once NifL dimerizes, it can bind to the NifA hexamer, hence preventing NifA from binding to NifHp. This sequestration effect provides the clock's negative feedback loop that is essential for oscillations. Our hope is to put these modules on the E.coli chromosome using a BioBrick compatible Arabinose Landing Pad (our iGEM 2007 project) and a Leucine Landing Pad (a construct of a former Ninfa lab member, Dong Eun Chang). We will use E.coli strain NCM 1971, which has the nifHp driving lacZ on the chromosome. This way, we can test the amounts of NifA via Beta-galactosidase activity and test the amount of NifL via fluorescent microscopy.