Figure 1.

Schematic of PNA-clamp SMAP-2 assay. For this assay, the SMAP-2 primer design principle is engineered to allow amplification of all possible sequences dictated by the first two nucleotides in codon 12 of KRAS. PNA-clamp competitive probe is designed for the wild-type allele sequence. The greater stability of the PNA probe in hybridization inhibiting to SMAP-2 amplification, and consequently the wild-type allele amplification is suppressed. This effect is theoretically manifest at the initial elongating event from the turn-back primer on wild-type template (case 1) or on a folding primer-synthesized strand (case 2) also early in the reaction.