Abstract: The invention relates to fusion proteins comprising at least three domains, where a first domain facilitates membrane localization of the fusion protein in a cellular context, and a second domain has or presumably has a ligand-binding function of a nuclear receptor, a third domain has an activity able to activate a signal pathway connected to a Ras protein in a cell, characterized in that when there is a lack of binding or, alternatively, when there is binding of ligand to the second domain the third domain cannot exert its activity to activate a signal pathway connected to a Ras protein in a cell, despite membrane localization. It additionally comprises inter alia cells which comprise such fusion proteins, assay methods using such cells, which are used inter alia for detecting specific interactions between ligand-binding sections of nuclear receptors and ligands, and kits for use in these assays.

Abstract: The invention relates to cells which comprise a membrane receptor which comprises a ligand-binding section, a membrane-localization signal and a mediator section, and which is characterized in that only when there is binding or, alternatively, only when there is a lack of binding of a ligand to the ligand-binding section of the membrane receptor is a structural change brought about with effects on the mediator section to result in binding of an effector protein or polypeptide, which is capable of activating a Ras or Ras-like signal pathway in the cell, to the component of the membrane, where appropriate via other proteins or polypeptides (adaptors). It further relates to assay methods employing these cells, which are used, inter alia, to detect specific interactions between said membrane receptor and a ligand, and kits for use in these assays.