DNA rearrangements in prokaryotes and eukaryotes.
One of the most distinctive mechanisms where DNA structure is involved are rearrangements of DNA. Three processes are distinguished:
During homologous recombination in a cell containing more than one copy of a given chromosome one copy can combine with corresponding segments of the other. This kind of recombination is ultimately dependent upon the DNA sequence homology between the two copies. Numerous models have been proposed for the mechanism of homologous recombination. A key intermediate in many of these is the Holliday juction. In Prokaryotas proteins involved in homologous recombination are encoded by genes recA, recB, recC and recD. Complex of proteins recBCD scans the chromosome searching for the special sequence called a chi site. After finding the site the recBCD complex cuts close to the spot.
Gene conversion leads to producing two copies of one „gene" while the other copy is destroyed.
Illegitimate recombination is a class of DNA rearrangement which is not dependent upon sequence homology. This kind of recombination is found to be important for movement of transposons and insertion of retroviral genomes into a host genome.
In every case of DNA rearrangement DNA forms unusual structures. Sharp bends and Holliday structures are the most distinctive ones.