These two receptors provide the opportunity for applying the powerful molecular genetic methodologies availabe in yeast towards understanding the mechanisms underlying signalling and regulation of this family of receptors. Our main focus has been on the endocytic down regulation of these receptors. By selective removal, endocytosis regulates abundance and cell surface distribution of receptor. Endocytosis has been studied for two decades in mammalian cell system and although gross features of membrane flow and intracellular traffic are understood, the molecular mechanisms underlying this transport remain largely obscure. We are trying to unravel this complexity by using a genetic approach in yeast, that is through the isolation of mutants that block the endocytic pathway.
New mutants map to the receptor gene as well as to other genes.
Mutations in the receptor serve to identify the signals on the receptor protein that direct uptake. Mutations in new genes provide a powerful way of identifying the individual protein components of the cellular apparatus which catalyzes endocytosis. Based upon the high conservation between yeast and mammals of proteins involved in other fundamental cellular processes, we expect that the proteins that we identify as catalyzing and regulating endocytosis in yeast will allow isolation of mammalian counterparts. The effects on localization of the a-factor receptor of a mutation in one of these newly identifed genes is shown below. In wild-type cells, endocytosis transports surface receptor to the lysosome.