Perfect interstranded triplexes that can potentially arise in the proviral DNA of wide-spread bovine retroviruses like as bovine leukemia virus (BLV) and bovine immunodeficiency virus (BIV) have been determined. In the BLV and BIV genomes 2 and 5 fragments respectively were found to form triple helixes under acidic conditions. One of those fragments that is localized on the BLV gag gene can exist as cruciform structure too. Experimentally the existence of triplexes is confirmed by atomic force microscopic visualization of supercoiled pGEMEX DNA for which genome 6 fragments are found with mirror symmetry that is necessary for intramolecular triplex formation. The diagrams of triplexes (one of the elements of signaling genome function) localization on the genome of bovine retroviruses are obtained.
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