Comprehensive screening of the human KRAS2 gene for sequence variants

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Abstract
To search for mutations in the human KRAS2 oncogene, we have analyzed polymerase chain reaction (PCR) fragments by denaturing gradient gel electrophoresis. We used six different PCR fragments to screen the five coding exons of this gene as well as the splice sites. GC clamps were added to each fragment by means of heteroduplex extension. We infer, from a theoretical analysis in which we employed the computer programs MELT and SQHTX, that virtually any mutation affecting one or a few base pairs in the coding exons or splice sites will be detectable. Thus the system that we describe should allow comprehensive detection of mutations throughout the coding exons and splice sites of the KRAS2 gene. As an example, we show that missense mutations at codons 12, 13, and 61 can be detected; mutant KRAS2 genes isolated from human tumors have been found to contain mutations only at these codons. We also report the discovery of three new polymorphic loci in the KRAS2 gene. We show that PCR reactions containing two or three fragments can be screened in a single lane of a denaturing gradient gel; this dramatically increases the number of base pairs that can be screened per gel.