Translesion synthesis, or molecular steeplechase

The review is devoted to the latest achievements in studying SOS mutagenesi s and translesion synthesis (DNA synthesis on damaged templates). A group o f novel DNA polymerases (proteins of the UmuC family) have been found, capa ble of bypassing the replication block caused by a lethal lesion in the tem plate. A special role of the steric factor in selection of the complementar y nucleotide at the active center of DNA polymerase is shown.