Mutation Via DNA Repair
Cytosine residues can lose their amino group with replacement by an oxygen. In the process, cytosine is converted to a uracil. Uracil does not pair well with the guanine that was opposite the cytosine so this base pair is recognized by the DNA repair enzymes as a mismatch. Since uracil is not a normal DNA base, it is removed and the repair system restores the original base pair of guanine - cytosine.
When 5-methylcytosine is deaminated, it becomes thymine which is a normal DNA base. However, thymine does not pair well with the guanine so this base pair is recognized as a mismatch. The repair system cannot distinguish one of the bases as not correct so the repair is 50% to G:C and 50% to the mutant form A:T.
This document maintained by Robert J. Huskey.
Last update on November 19, 1999.
