Model for the function of Rei1 at the exit of large ribosomal subunit biogenesis. Arx1, Alb1, and Tif6 are shuttling pre-60S factors that load on the precursors of the large ribosomal subunit in the nucleus and dissociate from the particles in the cytoplasm. At this last stage in biogenesis, the late ribosomal protein Rpl24 and the pre-60S factor Rei1 load on the particle. Rei1 triggers the Kap121-dependent recycling of Arx1 and Alb1 and subsequent dissociation and return of Tif6 to the nucleus. In the absence of Rei1, an Arx1, Alb1-containing subcomplex accumulates in the cytoplasm, which inhibits the dissociation of Tif6 from pre-60S particles. Thus, Tif6 antiassociation activity prevents the participation of novel large ribosomal subunits to translation initiation, and the lack of nuclear Tif6 results in pre-60S maturation defects.
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