Figure 2.

Identification of a single-nucleotide replacement by MALDI-MS analysis of four complementary base-specific cleavages.Each panel details one of the cleavage reactions (i.e., C- and U-specific cleavage using RNase-A on dT- and dC-incorporating transcripts of both strands) and includes the spectral changes that result from the substitution of a G (wt allele) for an A (mutant allele) as well as a comparison of the corresponding portions of the spectra obtained for three samples with a different genotype (black, homozygous wt; blue, heterozygous; green, homozygous substitution).Arrows indicate the predicted spectral changes that can be observed in the display.The 3326.1-Da peak in the C-reverse reaction does not disappear, because two wild-type fragments coincide at that spectral position, only one of which is affected by the mutation. Further spectral changes visible in the C and T-specific reverse reaction relate to an additional sequence change present in the displayed sample amplicon.