FucA1 is the only archaeal a-L-fucosidase gene identified so far; hence, it is probably the result of a horizontal gene transfer event in S.solfataricus. However, since there are no a-fucosidases genes regulated by programmed frameshifting in Bacteria and Eukarya, it is tempting to speculate that this sophisticated mechanism of translational regulation preexisted in S.solfataricus and it was applied to the fucosidase gene for physiological reasons. The identification of other genes interrupted by À1 frameshifts in S.solfataricus would open the possibility that they are regulated by programmed À1 frameshifting. Recently, the computational analysis of prokaryotic genomes revealed that seven Archaea harbour interrupted coding sequences, but S.solfataricus is not included in this study (40) . A computational analysis on several archaeal genomes revealed that 34 interrupted genes are present in the genome of S.solfataricus, 11 of these genes are composed by two ORFs separated by À1 frameshifting and could be expressed by recoding (B. Cobucci-Ponzano, M. Rossi and M. Moracci, manuscript in preparation).