The mutant Ssa-fuc B was prepared by site-directed mutagenesis from the vector pGEX-11867/3060, by using the same site-directed mutagenesis kit described above. The synthetic oligonucleotides used were FucA1sm-rev (described above) and the following mutagenic oligonucleotide: Fuc-B, 5 0 -GAACACCAATATCACCTAAAGAAGTTCGGCCC-AGT-3 0 , where the mismatched nucleotides are underlined. Direct sequencing identified the plasmid containing the desired mutations and the mutant gene, named fucA1 B , was completely re-sequenced. The enzymatic characterization of Ssa-fuc B was performed as described previously (24, 27) .