Base-specific cleavage and MALDI-TOF based discovery of the mutation G→A at position 356 in a 748-bp amplicon of the glycerol kinase gene (glpK). Mutation-specific signal changes as described in the text are highlighted and enlarged. (A) Overlay of mass spectra resulting from the T-specific cleavage reaction of the forward RNA transcript of the wild-type E. coli-K12 strain and the mutant isolate G1-A. Mutation-specific signal changes at 6813.2 Da and 6829.2 Da. (B) Overlay of mass spectra resulting from the T-specific cleavage reaction of the reverse RNA transcript of the wild-type E. coli-K12 strain and the mutant isolate G1-A. Mutation-specific signal changes at 1594.0 Da and 2830.8 Da. (C) Overlay of mass spectra resulting from the C-specific cleavage reaction of the forward RNA transcript of the wild-type E. coli-K12 strain and a mutant isolate G1-A. Intensity changes of mutation-specific mass signals at 1936.2 Da and 1952.2 Da. (D) Verification of the mutation by MALDI-TOF-based genotyping. A G-allele-specific extend product is detected in the wild-type E. coli-K12 strain at 6125.2 Da. The corresponding mutant C allele is detected at 6398.2 Da in clone G1-A.