In Saccharomyces cerevisiae, mRNA transcripts with premature termination codons 
are targeted for deadenylation independent decapping and 5' to 3' decay in a 
quality control pathway termed nonsense-mediated decay (NMD). Critical factors 
in NMD include Upf1, Upf2, and Upf3, as well as the decapping enzyme, Dcp2/Dcp1. 
Loss of Upf2 or Upf3 leads to the accumulation of not only Upf1 and Dcp2 in 
P-bodies, but also of the decapping-activators Pat1, Dhh1, and Lsm1. An 
interaction between Upf1 and Dcp2 has been identified, which might recruit Dcp2 
to the NMD decapping complex. To determine the nature and significance of the 
Dcp2-Upf1 interaction, we utilized the yeast two-hybrid assay to assess Upf1 
interactions with various mRNA decapping factors. We find that although Dcp2 can 
interact with Upf1, this interaction is indirect and is largely dependent on the 
Edc3 protein, which interacts with the N-terminal domain of Upf1 at an 
overlapping, but not identical, site as Upf2. We also found that Pat1 has an 
independent two-hybrid interaction with the N-terminus of Upf1. Assessment of 
both reporter and endogenous NMD transcripts suggest that the decapping 
stimulators, including Edc3 and Pat1, as well as Edc1 and Edc2, are not 
essential for NMD under normal conditions. This work defines a larger decapping 
complex involved in NMD, but indicates that components of that complex are not 
required for general NMD and might either regulate a subset of NMD transcripts 
or be essential for proper NMD under different environmental conditions.