Figure 3 : Simplified overviews of mismatch repair (MMR) and direct repair.

(A) After a mismatch made during replication is recognized in MMR, a nick is created by MLH1-PMS2 in the vicinity of the
mismatch. This enables the exonuclease EXO1 to remove DNA until it reaches the mismatch. The resulting gap is filled
with newly synthesized DNA by DNA polymerase and sealed by DNA ligases.
(B) Direct repair is mediated by O6-methylguanine methyltransferase (MGMT). It transfers the methyl group to a cysteine
residue of its own. This is a stoichiometric reaction as this transfer inactivates the MGMT molecule and targets it for
degradation (modified illustration of [129]).

Peters et al.Oncology Discovery  2014 2:3DOI : 10.7243/2052-6199-2-3