Palindromic sequences and A plus T-rich DNA elements promote illegitimate recombination in Nicotiana tabacum

Illegitimate recombination is the prevailing molecular mechanism for the in tegration of recombinant DNA into the genome of most eukaryotic systems and the generation of deletions by intrachromosomal recombination. We develope d a ?selectable marker system to screen for intrachromosomal illegitimate r ecombination events in order to assess the sequence and structure-specific requirements for illegitimate recombination in tobacco. In 12 illegitimate recombination products analysed, we found that all deletion termini localis e to sites of palindromic structures or to A+T-rich DNA elements. All delet ion termini showed microhomologies of two to six nucleotides. In three plan ts, the recombination products contained filler-DNA or an inversion of an e ndogenous segment. Our data strongly suggest that illegitimate recombinatio n in plants is mediated by a DNA synthesis-dependent process, and that this mechanism is promoted by DNA regions that can form palindromic structures or facilitate DNA unwinding. (C) 1999 Academic Press.