Proteasomes crossing the nuclear border.

Proteasomes localize to different compartments in eukaryotic cells, but the details of this dynamic distribution are poorly understood. Here, we discuss evidence linking proteasome activity to specific intranuclear locations and the potential mechanisms that may target these large proteolytic machines to the nucleus. Recent work has demonstrated the targeting of intact proteasome particles to newly formed nuclear compartments in a cell-free reconstitution assay. We discuss the difference between open and closed mitosis systems and the targeting of proteasomes to the nuclear periphery, as well as the nucleoplasm. Finally, we present a potential model for regulated assembly of the 26S proteasome holoenzyme inside the nucleus.