Western blots allowed us to identify a specific band $8.7 kDa heavier than that of the recombinant Ssa-fuc and experiments of translation in vitro showed that the wild-type gene expresses a full-length polypeptide exhibiting the same molecular mass of the recombinant protein. This demonstrates that the translational machinery of S.solfataricus is fully competent to perform programmed frameshifting. It seems likely that the observed discrepancy in molecular mass might arise from post-translational modifications that cannot be produced by the translation in vitro. Further experiments are required to characterize the a-L-fucosidase identified in S.solfataricus.