Draft #4, week 12, regulation by a LCR notes

- the LCR was first identified and characterized in Globin genes
- in the human visual system, an LCR has an important role in choosing either red or green opsin in a mutually exclusive manner
- each cone expresses only one pigment
- an LCR stochastically chooses one of the 2 promoter sites of the red-green pigment locus
- the physical interaction b/c the promoter and LCR activates the transcription
- b/c the red and green pigment genes are located on the X chromosome next to each other, this mutually exclusive acivation alone ensures monoallelic expression, you get equal # of red and green cones b/c its random, randomly interact w/ the 2 promoters
- monoallelic because it is on the X chromosome (cells randomly inactivate X), this is why males are more likely to be colorblind
- sequence comparison of the mouse and human genomes revealed a 2-kb homology (H) region far upstream of the MOR28 cluster
- negative feedback regulation ensures that one receptor-one olfactory neuron rule in mouse
- attachment of the H region to the truncated YAC constructs restored the expression of all the transgenes in the cluster
- crossed it with the transgenic that they made and found that they don’t express the same cell = its monoallelic, the LCR is intact