A NoLS, i.e. a sequence essential for nucleolar localization, is most probably a sequence involved in nucleolar retention by interacting with a nucleolar molecule such as B23 (Lechertier et al. 2007 ). Indeed, recent analyses of the intranuclear dynamics of proteins in living cells revealed that nuclear proteins could diVuse within the nucleoplasm (Phair and Misteli 2000; Sprague and McNally 2005) . As for the nucleolus, it was demonstrated that nucleolar proteins rapidly associate with and dissociate from nucleolar components in a continuous exchange with the nucleoplasm (Chen and Huang 2001; Dundr et al. 2004; Phair and Misteli 2000; Snaar et al. 2000) . There probably exist compartment-speciWc retention mechanisms for proteins in nuclear bodies, implying that the residency time of a particular molecule in a given nuclear body depends on its speciWc interactions (Misteli 2001) . In support of this possibility, we have recently shown that the fusion of a B23-interacting sequence with Wbrillarin makes it possible to re-localize Wbrillarin from the DFC to the GC of nucleoli where B23 is mainly localized (Lechertier et al. 2007) . Similarly, by fusing the B23-interacting sequence to MafG (part of the nuclear transcription factor NF-E2 composed of both MafG and p45), NF-E2 is redirected from the nucleoplasm to the GC. Therefore, interactions most probably govern the nuclear distribution of proteins and a NoLS is very likely a nucleolar molecule-interacting sequence.