Yeast cells engineered to produce pheromone system protein surrogates, and uses therefor

DETAILED DESCRIPTION In the present invention, a yeast cell is engineered to express an exogenous protein which is, however, capable of substituting for a yeast protein which is involved in the post-translational modification, transport, recognition or signal transduction of a yeast pheromone, sufficiently, to be able, at least under some circumstances, to carry out that role of the yeast protein.
For the sake of convenience, these yeast proteins will be referred to as "pheromone system proteins" (PSP), and their cognate non-yeast proteins as PSP surrogates.
The pheromone system of a yeast cell is thus subverted so that the response of the cell to a yeast pheromone is at least partially determined by the activity of the surrogate PSP.
In a preferred embodiment, the cognate yeast PSP is not produced in functional form, so that the response is essentially entirely dependent on the activity of the surrogate PSP.
Such yeast cells may be used to identify drugs which inhibit or activate, to a detectable degree, the ability of the surrogate to substitute for the cognate yeast PSP.
To screen for an inhibitor, a normally functional surrogate is expressed, and the presence of an inhibitor is indicated by a depression of the cellular response.
To screen for an activator, a surrogate functional in yeast, or one normally not functional in yeast but which is activatable (the latter is preferred, to minimize background) is used, and the activator is detected through its elevation of the cellular response.
In a preferred embodiment, the candidate drug is a peptide, and the yeast cell is engineered to express the candidate drug as well as the surrogate PSP.
Another consideration is that with wild-type yeast cells, to achieve pheromone secretion and response, both .
alpha.
and a cells must be provided.
In some preferred embodiments, .
alpha.
cells are engineered to express .
alpha.
-factor receptor or a cells are engineered to express a-factor receptor.
These modified cells may be considered "autocrine" because they are "self-stimulatory"