What is the ras pathway?
The ras pathway is a signal transduction cascade. In the Drosophila eye the receptor Sevenless is borne by cells that have the potential to develop into R7 photoreceptors, the last of eight photoreceptors to differentiate in each ommatidium. Signals from the ligand Boss, a seven pass transmembrane protein that serves as the ligand for Sevenless, triggers autophosphorylation in the Sevenless receptor tyrosine kinase. Phosphorylated Sevenless binds the adaptor protein DRK which subsequently interacts with SOS, a guanine nucleotide-releasing protein, which then removes GDP from inactive RAS and substitutes GTP. The substitution of GTP for GDP activates RAS protein. Up to this point ras pathway proteins functions not as a soup of ingredients but as an ordered complex assembled in a successive fashion to the cytoplasmic tail of the receptor Sevenless. Signal amplification is not the object, but rather assembly of a multimolecular membrane associated protein complex. Subsequent events, the a
