Abstract: An in cellulo method for the screening of proteasome activity-modulating agents, includes the following steps of: a) bringing into contact the candidate agent with the yeast cell expressing in their nucleus a fusion protein comprising: (i) a p21 polypeptide selected from the p21WAF1/Cip1 polypeptide and the p21[6KR]WAF1/Cip1 polypeptide; and (ii) at least one detectable protein; b) quantifying the first detectable protein in the yeast cells, at the end of at least one predetermined time interval after bringing into contact the candidate agent with the cells; c) comparing the value obtained at the step (b) with a control value obtained when the step (a) is performed in the absence of the candidate agent.

Abstract: A method for screening agents modulating I?B? protein ubiquitination by a functional ubiquitin ligase protein complex containing ?-TrCP protein, the method including the following steps: (a) bringing into contact a candidate agent to be tested with recombinant yeast cells that express in their nucleus: (i) a fusion protein including the I?B? polypeptide and at least one first detectable protein; and (ii) a protein containing the ?-TrCP polypeptide; (b) quantifying the first detectable protein in the yeast cells, at the end of at least one predetermined period of time after bringing the candidate agent into contact with the cells; (c) comparing the result obtained in step (b) with a control result obtained when step (a) is carried out in the absence of the candidate.