A viable hypomorphic allele of the essential IMP3 gene reveals novel protein functions in Saccharomyces cerevisiae.

Bruno Cosnier,Olivier Namy,Antonin Morillon,Marta Kwapisz,Céline Fabret,Sylvie Hermann-Le Denmat,Isabelle Hatin,Jean-Pierre Rousset,Steven R Ellis

doi:10.1371/journal.pone.0019500

Abstract

In Saccharomyces cerevisiae, the essential IMP3 gene encodes a component of the SSU processome, a large ribonucleoprotein complex required for processing of small ribosomal subunit RNA precursors. Mutation of the IMP3 termination codon to a sense codon resulted in a viable mutant allele producing a C-terminal elongated form of the Imp3 protein. A strain expressing the mutant allele displayed ribosome biogenesis defects equivalent to IMP3 depletion. This hypomorphic allele represented a unique opportunity to investigate and better understand the Imp3p functions. We demonstrated that the +1 frameshifting was increased in the mutant strain. Further characterizations revealed involvement of the Imp3 protein in DNA repair and telomere length control, pointing to a functional relationship between both pathways and ribosome biogenesis.

Highlights

In Saccharomyces cerevisiae, the essential IMP3 gene encodes a 183 amino acid component of the small ribosomal subunit (SSU) processome, which is required for pre-18S rRNA processing
Generation of a viable mutant allele of IMP3 In the course of studying translation termination accuracy at the stop codon of the essential IMP3 gene of S. cerevisiae, we constructed a mutant allele of IMP3 where the endogenous TAA stop codon was changed to a glutamine codon (CAA)
To construct the corresponding strain (IMPQ strain), the mutant allele was first obtained on a vector by site-directed mutagenesis of wild-type IMP3 gene and was inserted at the endogenous locus of a FS1 strain

Summary

Introduction

In Saccharomyces cerevisiae, the essential IMP3 gene encodes a 183 amino acid component of the small ribosomal subunit (SSU) processome, which is required for pre-18S rRNA processing. This large ribonucleoprotein complex is composed of the nascent 35S pre-rRNA, the small nucleolar RNA U3 and of about 50 proteins. The Imp protein interacts with Mpp10p (Imp stands for ‘‘interacting with Mpp10p’’) and mediates interactions of Imp4p and Mpp10p with the U3 snoRNA [3,4]. The Imp and Imp proteins apparently increase the stability of the otherwise unstable U3 – ETS RNA hybrid [5,6]. Yeast and human Imp proteins display ,50% identity and 65% similarity, and their role in pre-rRNA processing is evolutionary conserved [7]

Methods

Results

Conclusion