Left-handed Z-DNA and intramolecular triplex formation at the site of an unequal sister chromatid exchange

摘要: An unequal sister chromatid exchange (USCE) in the mouse myeloma cell line MPC-11 between 3' regions of C gamma 2a and 2b heavy chain genes results duplication gene generation a novel recombination joint. The USCE occurs (TC)n tracts adjacent to alternating purine-pyrimidine tracts. We have investigated capacity both donor recombinant product involved this event adopt left-handed Z-DNA intramolecular triplexes. chemical probing with diethylpyrocarbonate osmium tetroxide at base pair level demonstrate that under influence negative supercoiling these plasmids can neutral pH, oligopurine.oligopyrimidine (pur.pyr) triplexes low pH (less than or equal 6.0). At intermediate values, mixtures structures are present. Increasing superhelical density plasmid does not increase amount triplex present indicating presence long segments pur.pyr tract prevents formation. In summary, we conclude sequences form either an will predominate physiological conditions. which site suggests formation structure may enhance