We developed mobility shift analysis of single-stranded DNAs on neutral polyacrylamide gel electrophoresis to detect DNA polymorphisms. This method follows digestion of genomic DNA with restriction endonucleases, denaturation in alkaline solution, and electrophoresis on a neutral polyacrylamide gel. After transfer to a nylon membrane, the mobility shift due to a nucleotide substitution of a single-stranded DNA fragment could be detected by hybridization with a nick-translated DNA fragment or more clearly with RNA copies synthesized on each strand of the DNA fragment as probes. As the mobility shift caused by nucleotide substitutions might be due to a conformational change of single-stranded DNAs, we designate the features of singlestranded DNAs as single-strand conformation polymorphisms (SSCPs). Like restriction fragment length polymorphisms (RFLPs), SSCPs were found to be allelic variants of true Mendelian traits, and therefore they should be useful genetic markers. Moreover, SSCP analysis has the advantage over RFLP analysis that it can detect DNA polymorphisms and point mutations at a variety of positions in DNA fragments. Since

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One type of aberration of DNA found in human cancers is loss of heterozygosity at chromosomal loci. This loss suggests that inactivation of particular genes is involved in the genesis of cancer cells. We have analyzed tumor DNA and normal DNA from eight patients with malignant melanomas using 24 polymorphic DNA probes and detected loss of heterozygosity in three patients at five loci on four different chromosomes. These results indicate that the frequency of loss of heterozygosity at chromosomal loci is relatively high in malignant melanomas, but that the regions lost are not restricted to specific chromosomes.

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