The nematode antizymes were analyzed for the presence of possible 5¢ or 3¢ stimulators¯anking the core frameshift site. Computer RNA folding programs did not identify any potentially interesting structure. More importantly, phylogenetic analysis with the ®ve identi®ed nematode antizymes failed to identify any conservation of primary RNA sequence (or for that matter potential secondary structure) outside of the core region that is shared between two or more members. This could indicate that no such extra cis-acting stimulators exist in nematode antizymes or that they are located in a very different place within the mRNA, for example the 3¢ untranslated region (the latter suggestion is not supported by our sequence analysis).