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PCR preferential amplification consists of the inefficient amplification of one allele in a heterozygous sample. Here, we report the isolation of a GC-rich human minisatellite, MsH43, that undergoes allelic preferential amplification during PCR. This effect requires the existence of a (TGGGGC) 4 motif that is able to form a G-quadruplex in the presence of K þ . This structure interferes with the DNA synthesis of the alleles harbouring this motif during PCR The present results are the first demonstration that the formation of G-quadruplex can be one of the mechanisms involved in some kinds of preferential amplification.

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We report the isolation of a new low polymorphic GC-rich human minisatellite locus (\lsH42) that contains different recombination motifs and is homologous to sequences involved in immunoglobulin class-switching. Furthermore, we show that MsH42 undergoes slipped-strand mispairing during PCR indicating its ability to generate single-stranded loops. Specific DNA-protein complexes were detected in band-shifting experiments using nuclear extracts from mouse testes and human NC-37 cells. The possible implications of this minisatellite in recombination events is discussed.