PCI complexes: pretty complex interactions in diverse signaling pathways

Three protein complexes (the proteasome regulatory lid, the COP9 signalosom e and eukaryotic translation initiation factor 3) contain protein subunits with a well defined protein domain, the PCI domain. At least two (the COP9 signalosome and the lid) appear to share a common evolutionary origin. Rece nt advances in our understanding of the structure and function of the three complexes point to intriguing and unanticipated connections between the ce llular functions performed by these three protein assemblies, especially be tween translation initiation and proteolytic protein degradation.