Analysis of intrachromosomal homologous recombination in mammalian cell, using tandem repeat sequences

In all the organisms, homologous recombination (HR) is involved in fundamen tal processes such as genome diversification and DNA repair. Several strate gies can be devised to measure homologous recombination in mammalian cells. We present here the interest of using intrachromosomal tandem repeat seque nces to measure HR in mammalian cells and we discuss the differences with t he ectopic plasmids recombination. The present review focuses on the molecu lar mechanisms of HR between tandem repeats in mammalian cells. The possibi lity to use two different orientations of tandem repeats (direct or inverte d repeats) in parallel constitutes also an advantage. While inverted repeat s measure only events arising by strand exchange (gene conversion and cross ing over), direct repeats monitor strand exchange events and also non-conse rvative processes such as single strand annealing or replication slippage. In yeast, these processes depend on different pathways, most of them also e xisting in mammalian cells. These data permit to devise substrates adapted to specific questions about HR in mammalian cells. The effect of substrate structures (heterologies, insertions/deletions, GT repeats, transcription) and consequences of DNA double strand breaks induced by ionizing radiation or endonuclease (especially the rare-cutting endonuclease ISce-I) on HR are discussed. Finally, transgenic mouse models using tandem repeats are brief ly presented. (C) 1999 Elsevier Science B.V. All rights reserved.