The mutants in the slippery sequence of the wild-type gene fucA1 were prepared by site-directed mutagenesis from the vector pGEX-11867/3060, described previously (24, 27) . The synthetic oligonucleotides used (PRIMM) were the following: FucA1sm-rev, 5 0 -TTTAGGTGATATTGGTGTT-CTGGTCTATCT-3 0 ; FucA1sm-fwd, 5 0 -GAACACCAATAT-CACCTAAAGAATTCGGCCCA-3 0 ; FucA1tm-rev, 5 0 -AGG-TGATATTGGTGTTCTGGTCTATCTGGC-3 0 ; FucA1tm-fwd, 5 0 -CCAGAACACCAATATCACCTCAAGAACTCGGCCCA-GT-3 0 , where the mismatched nucleotides in the mutagenic primers are underlined. Direct sequencing identified the plasmids containing the desired mutations and the mutant genes, named fucA1 sm and fucA1 tm , were completely re-sequenced.