The mRNAs encoding wild-type fucA1 and its various mutants were obtained by in vitro run-off transcription. About 2 mg of each plasmid was linearized with BssHII and incubated with 50 U of T7 RNA polymerase for 1 h 30 min at 37 C. The transcription mixtures were then treated with 10 U of DNAseI (RNAse free) for 30 min. The transcribed RNAs were recovered by extracting the samples twice with phenol (pH 4.7) and once with phenol/chloroform 1:1 followed by precipitation with ethanol. The mRNAs were resuspended in DEPC-treated H 2 O at the approximate concentration of 0.6 pmol/ml.