Genetics under geothermal conditions: Homologous recombination in the archaeon Sulfolobus acidocaldarius
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Hyperthermophilic archaea differ radically from all model organisms with respect to their evolutionary history and the severe environmental conditions they require. This divergence raises questions as to whether their genetic processes also have unusual properties; but few of these processes have been analyzed in vivo. In the extreme thermoacidophile Sulfolobus acidocaldarius, a conjugational mechanism of DNA transfer enables recombination between chromosomal mutations to be quantified. Early studies of this system suggested a non-reciprocal mechanism in which donor sequences become incorporated into the recipient genome as short segments. Subsequent studies using electroporation found that synthetic oligonucleotides can recombine into this genome. When similar experiments used longer, duplex DNAs containing multiple, silent markers, the resulting recombinants often contained multiple replacement tracts, consistent with an unusual, "short-patch" mode of homologous recombination.