WHAT ARE THE PROPERTIES OF HOMOLOGOUS RECOMBINATION IN HYPERTHERMOPHILIC ARCHAEA?

S. acidocaldarius has a conjugational mechanism of DNA exchange that provides a convenient genetic assay for homologous recombination in the chromosome. Cells of two stable auxotrophic mutants are simply mixed together and plated on minimal medium; recombinants appear as prototrophic colonies. The process requires cell-cell contact but does not require a conjugal plasmid or specialized donor strain, and it initiates rapidly in liquid medium [see publications 1 and 7].

Using this assay, we found that intragenic recombination within the S. acidocaldarius pyrE gene is unexpectedly frequent. When randomly chosen pyrE mutants were paired and mated, very few pairs failed to form recombinants. Sequence analysis of a few mutants showed that recombination was readily detected between mutations only 28 bp apart. A statistical analysis of many more crosses yielded an estimate of only 14 bp for the separation required [publication 13] These results suggest that homologous recombination in S. acidocaldarius may be so active as to preclude classical linkage among chromosomal genes [publication 21].

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