title: Nascent peptide-dependent translation arrest leads to Not4p-mediated protein degradation by the proteasome.
abstract: The potentially deleterious effects of aberrant mRNA lacking a termination codon (nonstop mRNA) are ameliorated by translation arrest, proteasome-mediated protein destabilization, and rapid mRNA degradation. Because polylysine synthesis via translation of the poly(A) mRNA tail leads to translation arrest and protein degradation by the proteasome, we examined the effects of other amino acid sequences. Insertion of 12 consecutive basic amino acids between GFP and HIS3 reporter genes, but not a stem-loop structure, resulted in degradation of the truncated green fluorescent protein (GFP) products by the proteasome. Translation arrest products derived from GFP-R12-FLAG-HIS3 or GFP-K12-FLAG-HIS3 mRNA were detected in a not4Delta mutant, and MG132 treatment did not affect the levels of the truncated arrest products. Deletion of other components of the Ccr4-Not complex did not increase the levels of the translation arrest products or reporter mRNAs. A L35A substitution in the Not4p RING finger domain, which disrupted its interaction with the Ubc4/Ubc5 E2 enzyme and its activity as an ubiquitin-protein ligase, also abrogated the degradation of arrest products. These results suggest that Not4p, a component of the Ccr4-Not complex, may act as an E3 ubiquitin-protein ligase for translation arrest products. The results let us propose that the interaction between basic amino acid residues and the negatively charged exit tunnel of the ribosome leads to translation arrest followed by Not4p-mediated ubiquitination and protein degradation by the proteasome.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Lyudmila N
authors.initials: LN
authors.lastname: Dimitrova
authors.forename: Kazushige
authors.initials: K
authors.lastname: Kuroha
authors.forename: Tsuyako
authors.initials: T
authors.lastname: Tatematsu
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Inada
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014176:Protein Biosynthesis; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D010455:Peptides; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C086923:MOT2 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex