Noticeably, this is the only fucosidase gene expressed by programmed À1 frameshifting. Among carbohydrate active enzymes, the only example of expression through this recoding mechanism is that reported for a gene encoding for a a(1,2)-fucosyltransferase from Helicobacter pylori that is interrupted by a À1 frameshifting (38) . In this case, the expression by programmed frameshifting would lead to a functional enzyme synthesizing components of the surface lipopolysaccharides to evade the human immune defensive system. It is hard to parallel this model to fucA1. Nevertheless, the monosaccharide fucose is involved in a variety of biological functions (39) . Therefore, the a-L-fucosidase might play a role in the metabolism of fucosylated oligosaccharides; experiments are currently in progress to knockout the wild-type fucA1 gene and to insert constitutive functional mutants of this gene in S.solfataricus.