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Abstract:
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Translation is an essential and fundamental process that coverts genetic codes into functional polypeptides by an apparatus called ribosome . In eukaryotic cells , ribosomes are composed of two subunits : the large (60S ) subunit and small (40S ) subunits . In Saccharomyces cerevisiae , ribosome biogenesis is complex and requires the involvement of over ~170 trans -acting factors . As a growing number of factors were identified related to this essential metabolic pathway , our lab has contributed to functional characterization of the late 60S subunit biogenesis pathway that centers on Nmd3p . This work particularly focuses on characterizing of the nuclear shuttling trans -acting factor Arx1p found in the Nmd3p -60S subunit particle . A working model that describes how Rei1p , another cytosolic trans -acting factor , recycles Arx1p is presented . This work also shows a similar mode of Arx1p recycling by the Hsp40 J -protein , Jjj1p . Furthermore , I have investigated functional interplay between Arx1p and Rpl25p , a 60S ribosomal protein at the polypeptide exit tunnel . These findings further reveal the involvement of Arx1p at the polypeptide exit tunnel in mediating association of other factors with 60S subunits . Beyond its function at the polypeptide exit tunnel , this work also focuses on a function for Arx1p in the export of 60S subunits . In yeast and higher eukaryotes , 60S subunit export depends on the export adaptor Nmd3p via Crm1 -dependent pathway . I show that ARX1 interacts with the NES of Nmd3p and nucleoporins . From these results , I propose that Arx1p acts as another export receptor to facilitate 60S subunit export . |