BACKGROUND: The nonsense-mediated mRNA decay (NMD) pathway promotes the rapid 
degradation of mRNAs containing premature termination codons (PTCs). In yeast 
Saccharomyces cerevisiae, the activity of the NMD pathway depends on the 
recognition of the PTC by the translational machinery. Translation termination 
factors eRF1 (Sup45) and eRF3 (Sup35) participate not only in the last step of 
protein synthesis but also in mRNA degradation and translation initiation via 
interaction with such proteins as Pab1, Upf1, Upf2 and Upf3.
RESULTS: In this work we have used previously isolated sup45 mutants of S. 
cerevisiae to characterize degradation of aberrant mRNA in conditions when 
translation termination is impaired. We have sequenced his7-1, lys9-A21 and 
trp1-289 alleles which are frequently used for analysis of nonsense suppression. 
We have established that sup45 nonsense and missense mutations lead to 
accumulation of his7-1 mRNA and CYH2 pre-mRNA. Remarkably, deletion of the UPF1 
gene suppresses some sup45 phenotypes. In particular, sup45-n upf1Delta double 
mutants were less temperature sensitive, and more resistant to paromomycin than 
sup45 single mutants. In addition, deletion of either UPF2 or UPF3 restored 
viability of sup45-n double mutants.
CONCLUSION: This is the first demonstration that sup45 mutations do not only 
change translation fidelity but also acts by causing a change in mRNA stability.