Spontaneous DNA-DNA interaction of homologous duplexes and factors affecting the result of heteroduplex formation.

Mutation detection and mismatch repair investigations based on heteroduplex formation require a linear DNA structure. DNA branching, described previously under physiological conditions, has been analysed in the heteroduplex formation process. Symmetrical chi-structures were detected after heteroduplex formation by gel electrophoresis and electron microscopy. Buffer composition, DNA concentration and duplex end-sequences influence DNA branching. Duplexes with homologous central regions but non-complementary ends do not form hybrid heteroduplexes or hybrid Holliday junctions. Our results explain the requirements for efficient heteroduplex formation, which were previously determined empirically: special solution composition, optimal DNA concentration and GC clamps. This provides the theoretical background for further optimisation of the procedure.