Biopolymers and cell. 2001; 17 (6): 487 - 500

The molecular mechanisms derivation of mutation bases alteration after a postreplication SOS-reparation an DNA contaning thymine dimers

H. A. Grebneva

Molecular mechanisms of mutation of bases alteration after the postreplication SOS-reparation of DNA containing thymine dimers The postreplication SOS-reparation at which the postreplicative gaps are built up de novo is analyzed. The DNA molecule, containing in one of its chains thymine dimers with nucleotide bases in rare tautomeric forms, which can influence the character of base pairing, is considered. Depending on the type of the dimers formed the postreplication SOS-reparation may lead to 1) transition or ho¬mologous transversion; 2) appearance of one-nucleotide gap, cau¬sing a shift mutation of a reading frame; or 3) absence of mutation at all. It has been concluded that the dimers studied (cyclic butane or 6—4 adducts) cause the targeted mutagenesis. The assumption has been made that the SOS-system induction, decreasing proof¬reading functions (in comparison with polymerase) weakens the control over the matrix DNA bases to be in the canonical tautomeric forms.