[On the origin of extra bands at MCT118 typing]

In order to probe the origin of extra bands that appear frequently in MCT118 typing, we examined the extra bands by Dual PCR, Asymmetric PCR and PCR-SSCP method. It is conceivable that two extra bands of 16-18 type are DNA heteroduplexes that result from 16 and 18 allele bands at mutual cross-annealing. The extra bands can easily take the higher-order structure due to a non-complimentary sequence of bases. Consequently, the distances that extra bands travel in electrophoresis depend on a gel composition. Because the extra bands can be distinguished from the original allele bands by electrophoresis using different gel composition, it will not become an obstacle at the typing.