To measure the global efficiency of frameshifting in the two sites of the wild-type gene fucA1 we analysed the total extracts of E.coli by western blot using anti-GST antibodies ( Figure 2F ). Two bands with marked different electrophoretic mobility were observed: the polypeptide of 78.7 ± 1.1 kDa migrated like GST-Ssa-fuc fusion and was identified as originated from frameshifting in either site A or B of fucA1. The protein of 38.1 ± 1.2 kDa, which is not expressed by the mutant gene fucA1 A (not shown), had an electrophoretic mobility compatible with GST fused to the polypeptide encoded by the ORF SSO11867 solely (27 and 9.6 kDa, respectively). This polypeptide originated from the translational termination of the ribosome at the OCH codon of the fucA1 N-terminal ORF ( Figure 1A) . The calculated ratio of frameshifting to the termination products was 5%.