Difference between revisions of "Part:BBa K779608"

Latest revision as of 04:38, 11 October 2012

Hef1a-HH-mKate Mammoblock Device

This part introduces in vivo hammerhead ribozymes to iGEM and the registry. Hammerhead ribozymes are self-cutting strands of catalytic RNA. After a hammerhead ribozyme is transcribed in a cell, it folds into a secondary structure, which causes self-cleavage. Because of their RNA-cleaving function, hammerheads may be used to regulate protein expression and to make other RNA parts. For more information on hammerheads in general, see http://en.wikipedia.org/wiki/Hammerhead_ribozyme .

This part consists of a constitutive promoter Hef1A with a hammerhead ribozyme attached to an mKate florescent protein for reporting purposes. This part is designed to show that hammerheads can self-cleave in a mammalian environment. After the hammerhead-mKate sequence is transcribed, the mRNA sequence should cleave, preventing the transcription of mKate. Successful cleavage can be verified by comparing fluorescence levels to a constitutive mKate control.
Testing a 5' Hammerhead appended to mKate driven by a Hef1A promoter :

The circuit above shows Hef1A constitutive promoter driving an mKate (red fluorescent protein), which serves as our positive control. We also tested Hef1A constitutive promoter driving a hammerhead before an mKate. Once the hammerhead is transcribed, one could assume that since it is self cleaving, the mRNA will be cleaved and the mKate will not be expressed. We also appended the Hammerhead at the 3' end of the mKate mRNA and expect similar results.
Above image: Key: Red: mKate, Blue: mKate-Hammerhead, Green: Hammerhead-mKate. 100,000 HEK293 cells were transfected with equimolar amounts of Hef1a:TagBFP, as a transfection marker, and one of the following: Hef1a:mKate, Hef1a:Hammmerhead-mKate, and Hef1a:mKate-Hammerhead. 48 hrs later, cells were harvested and analyzed by flow cytometry until 10,000 events were recorded. The histograms are gated on the blue population of cells, meaning that we are examining red fluorescence (mKate signal) in cells that also received the TagBFP DNA. There is less red fluorescence in the hammerhead constructs compared to the Hef1a: mKate. This suggests that the hammerhead ribozymes could be cleaving the mRNA.

Sequence and Features