Ecm1 is a new pre-ribosomal factor involved in pre-60S particle export

Abstract

In eukaryotes, ribosome biogenesis is a highly conserved process that starts in the nucleus and ends in the cytoplasm. In actively growing yeast cells, it is estimated that each nuclear pore complex (NPC) contributes to the export of about 25 pre-ribosomal particles per minute. Such an extremely active process requires several redundant export receptors for the pre-60S particles. Here, we report the identification of a novel pre-60S factor, Ecm1, which partially acts like Arx1 and becomes essential when the NPC function is affected. Ecm1 depletion, combined with the deletion of NPC components led to pre-60S retention in the nucleus. Functional links that we identified between Ecm1, 60S biogenesis, pre-60S export, and the NPC were correlated with physical interactions of Ecm1 with pre-60S particles and nucleoporins. These results support that Ecm1 is an additional factor involved in pre-60S export. While Ecm1 and Arx1 have redundant functions, overproduction of either one could not complement the absence of the other, whereas overproduction of Mex67 was able to partially restore the growth defect resulting from the absence of Ecm1 or Arx1. These data highlight the involvement of many factors acting together to export pre-60S particles.

Ribosome Biogenesis in the YeastSaccharomyces cerevisiae

“…At least five proteins (Arx1, Bud20, Ecm1, Mex67, and Nmd3) function together to enable nuclear export of pre-60S subunits Gadal et al 2001b;Bradatsch et al 2007;Yao et al 2007Yao et al , 2010Hung et al 2008;Bassler et al 2012).…”

Mechanistic insight into eukaryotic 60S ribosomal subunit biogenesis by cryo-electron microscopy

“…While small molecules can diffuse through the pore freely, large macromolecules need to recruit export factors that help them pass through a meshwork formed by FG-rich repeats of nucleoporins that fill the channel at the center of the NPC (Grossman et al 2012). The nascent 60S particle acquires export competence by recruiting its full set of nuclear export factors, which include Nmd3, Mex67-Mtr2, Arx1, Bud20, and Ecm1 in yeast (Ho et al 2000b;Gadal et al 2001;Bradatsch et al 2007;Yao et al 2007Yao et al , 2010Hung et al 2008;Altvater et al 2012;Bassler et al 2012). The requirement for a large number of export factors may originate from the large size of the pre-60S subunit, which at more than 2 MDa molecular weight is among the largest cargoes transported through the NPC (Knockenhauer and Schwartz 2016).…”

Bcp1 Is the Nuclear Chaperone of Rpl23 in Saccharomyces cerevisiae

“…Consequently, the ribosomal proteins must be imported into the nucleus for assembly with the rRNAs. After ribosome assemblies have achieved a certain stage of maturation, export factors are loaded to direct these huge complexes to cross the nuclear membrane through the nuclear pore complexes (1)(2)(3)(4)(5)(6). In the cytoplasm, ribosomes undergo additional steps in the maturation process; the trans-acting factors that are exported with nascent ribosomal subunits need to be stripped off, additional ribosomal proteins are added, and in the case of the 40S subunit, the final rRNA processing occurs (7,8).…”