PgmNr Y3055: Protein quality control that regulates unassembled ribosomal proteins.

Authors:
M. Sung; R. Deshaies


Institutes
California Institute of Technology, Pasadena, CA.


Keyword: Protein Sorting and Turnover

Abstract:

Assembly of ribosomes accounts for a large fraction of total RNA and protein synthesis in yeast. All ribosomal subunits are present in assembled ribosomes at 1:1 stoichiometry, but it is anticipated that in synthesizing the ~80 proteins that form a ribosome, modest variations in expression must inevitably occur with some subunits expressed in modest excess over others. Ribosomal proteins produced in slight excess will not be able to assemble and are presumably degraded by a quality-control pathway(s) that senses unusable proteins. Given the major contribution of ribosome assembly to total cellular biosynthesis, such a quality-control pathway is likely to play a significant role in protein homeostasis. However, the responsible quality-control mechanisms remain poorly characterized. Here, we demonstrate that overexpression of multiple proteins of the small and large yeast ribosomal subunits is suppressed. Our studies reveal that ribosomal proteins that fail to assemble into ribosomes are rapidly distinguished from their assembled counterparts and are ubiquitinated and degraded by proteasome within the nuclear compartment.