The surveillance complex interacts with the translation release factors to enhance termination and degrade aberrant mRNAs

Abstract

The nonsense-mediated mRNA decay pathway is an example of an evolutionarily conserved surveillance pathway that rids the cell of transcripts that contain nonsense mutations. The product of the UPF1 gene is a necessary component of the putative surveillance complex that recognizes and degrades aberrant mRNAs. Recent results indicate that the Upf1p also enhances translation termination at a nonsense codon. The results presented here demonstrate that the yeast and human forms of the Upf1p interact with both eukaryotic translation termination factors eRF1 and eRF3. Consistent with Upf1p interacting with the eRFs, the Upf1p is found in the prion-like aggregates that contain eRF1 and eRF3 observed in yeast [PSI + ] strains. These results suggest that interaction of the Upf1p with the peptidyl release factors may be a key event in the assembly of the putative surveillance complex that enhances translation termination, monitors whether termination has occurred prematurely, and promotes degradation of aberrant transcripts.[Key Words: mRNA decay; translation termination; release factors; nonsense mutation; ribosome; mRNA surveillance]Received January 21, 1998; revised version accepted April 1, 1998. Recent studies have demonstrated that cells have evolved elaborate mechanisms to rid themselves of aberrant proteins and transcripts that can dominantly interfere with their normal functioning (He et

Rules that govern UPF1 binding to mRNA 3′ UTRs

“…The finding that the co-IP of HISeRF3(WT) with UPF1 was RNase A sensitive (Fig. 3A) although UPF1 binding directly to eRF3 (6,33,34) indicates that most of UPF1 binding is not to eRF3 but, presumably, to 3′ UTRs and their EJCs. We do not think that UPF1 binding is mediated by eRF3 binding to poly(A)-bound PABPC1 because data indicate a complex of UPF1−eRF3−PABPC1 cannot be detected by using purified proteins (6).…”

“…To begin to define when the process of translation-enhanced UPF1 binding to an NMD target occurs, it made sense to focus on the last step of translation given that translation termination defines the 3′ UTR. We focused on the requirement for eRF3 because it interacts directly with UPF1 during translation termination (6,33,34). To this end, HEK293T cells were transiently transfected with pcDNA-HIS-eRF3(WT) or pcDNA-HIS-eRF3(KAKA), which produce respectively histidine(HIS)-tagged wild-type (WT) eRF3 or HIStagged eRF3 harboring L69K, N72A, A73K, and F76A (KAKA) (6) or, as a control, pcDNA-HIS-LACZ, which produces mRNA that encodes HIS-tagged E. coli β-galactosidase mRNA.…”

Nonsense-mediated Decay of mRNA for the Selenoprotein Phospholipid Hydroperoxide Glutathione Peroxidase Is Detectable in Cultured Cells but Masked or Inhibited in Rat Tissues

“…For example, release factors, which are likely to be required for NMD (Czaplinski et al, 1998), may not be involved if the nascent PHGPx peptide fails to be released from its mRNA template when the Sec codon reaches the A site of the translating ribosome. A precedent for this is provided by the 22-codon upstream open reading frame (uORF2) of the human cytomegalovirus UL4 transcript leader.…”

SMG6 interacts with the exon junction complex via two conserved EJC-binding motifs (EBMs) required for nonsense-mediated mRNA decay

“…Current models for NMD suggest that UPF1 and SMG1 are recruited by ribosomes terminating translation prematurely through interactions with the eukaryotic release factors eRF1 and eRF3 (Czaplinski et al 1998;Kashima et al 2006). In the presence of UPF2 and/or UPF3, presumably bound to downstream EJCs on the mRNA, SMG1 phosphorylates UPF1; this in turn recruits SMG5, SMG6, and SMG7 (Denning et al 2001;Pal et al 2001;Yamashita et al 2001;Anders et al 2003;Chiu et al 2003;Ohnishi et al 2003;Fukuhara et al 2005).…”