In the Drosophila egg, during signalling through the epidermal growth facto
r (EGF) receptor, a conformational switch, which is dependent on mitogen-ac
tivated protein kinase (MAPK) leads to the Cf2 transcriptional repressor be
ing targeted for proteolysis. Recent work shows that this switch is catalys
ed by the Drosophila homologue of Pin1, a peptidyl-prolyl isomerase.