engleski

Palindromes as inducers of mitotic recombination in yeast

Recombination between repeated sequences distributed in the genome is a potential source of genetic instability leading to the formation of deletions, duplications, inversions and translocations. Inverted repeats, or palindromes, are important cis-acting genetic elements and present a special class of repeated sequences due to their ability to form secondary structures known as cruciformes and hairpins. Such structures could impede the DNA replication or could act as a substrate for resolvases, enzymes needed for the resolution of recombination intermediates. Genetic instability of palindromes has been demonstrated in different organisms from Escherichia coli to humans where it was found associated with several genetic diseases. Here we analyzed the ability of a 102 bp palindromic sequence to stimulate recombination in yeast Saccharomyces cerevisiae. We used two different assays for homologous recombination: plasmid integration and formation of intrachromosomal deletions between direct repeats ("pop-out"). Recombination between repeated copies of the CYC1 gene was stimulated 4 to 9-fold when the palindrome was inserted either within or between the homologous sequences. The same assay was used to determine the minimal size of a palindromic sequence that stimulates recombination. In plasmid integration assay, palindromic insertion was placed either in chromosomal or in plasmid copy of the CYC1 gene. Stimulation was observed only when the palindrome was present in the yeast chromosome, while when present on the plasmid molecule, it even decreased integration to homology. These results suggest that the palindrome-stimulated initiation of recombination depends on DNA replication, but they also indicate that palindromic sequences may influence subsequent step(s) of recombination process.

palindrome; recombination; yeast

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