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CRM1 is an export factor that, together with its adaptor NMd3, transports numerous cargo molecules from the nucleus to cytoplasm through the nuclear pore. in previous stud-ies, CRM1 and NMd3 were also detected in the nucleolus, but their localization with subnucleolar domains or participation in the activities of the nucleolus remain unclear. A new study by dr Marikki Laiho and colleagues confirmes that CRM1 and NMd3 co-localize with nucleolar marker proteins in the nucleo-lus. in particular, they found that nucleolar localization of these two proteins is markedly increased by inhibition of RNA polymerase i (Pol i) transcription. CRM1 nucleolar local-ization was shown to be dependent on its activity and the expression of NMd3, whereas NMd3 nucleolar localization was independent of CRM1. this suggests that NMd3 provides nucleolar tethering of CRM1. While inhibition of CRM1 by leptomycin B inhibited processing CRM1 and NMD3 localize to the nucleolus and affect rRNA synthesis Baoyan Bai, Henna M Moore, and Marikki Laiho of 28S rRNA, depletion of NMd3 did not, suggesting that their effects on 28S rRNA processing are distinct. Markedly, depletion of NMd3 and inhibition of CRM1 reduced the rate of pre-47S rRNA synthesis. However, their inactivation did not lead to nucleolar disinte-gration, a hallmark of Pol i transcription stress, suggesting that they do not directly regu-late transcription. taken together, the study results indicate that CRM1 and NMd3 have complex functions in pathways that couple rRNA synthetic and processing engines and that the rRNA synthesis rate may be adjusted according to proficiency in rRNA processing and export