Fig. 5. Binding to nos-2 3'UTR is essential for the translation suppression activity of MEX-3 and SPN-4. Two 8 bp direct repeats present in nos-2 3'UTR are critical for the binding of MEX-3 and SPN-4. (A) Alignment of the nos-2 3'UTR of the indicated species (D'Agostino et al., 2006). Only the region with two 8 bp direct repeats (DR1 and DR2; boxed) is shown. Stars indicate bases conserved in all three species. Sequences of mutations used in B,C are shown in red. (B) Electrophoretic mobility shifts by MBP:MEX-3 (top) and GST:SPN-4 (bottom) of the various mutant versions of radiolabeled nos-2 3'UTR. (C) Expression pattern of GFP:H2B in embryos of transgenic worms carrying the GFP:H2B:nos-2 3'UTR transgene bearing the indicated mutations, or following spn-4(RNAi) or mex-3(RNAi). The GFP:H2B distribution pattern in DR1 and DR2 is similar to that of spn-4(RNAi) and the pattern in DR1+DR2 is similar to that of mex-3(RNAi).