  Damaged or mismatched bases in DNA can be repaired by Base Excision Repair
(BER) enzymes that replace the defective base. Although the detailed molecular
structures of many BER enzymes are known, how they colocalize to lesions
remains unclear. One hypothesis involves charge transport (CT) along DNA
[Yavin, {\it et al.}, PNAS, {\bf 102}, 3546, (2005)]. In this CT mechanism,
electrons are released by recently adsorbed BER enzymes and travel along the
DNA. The electrons can scatter (by heterogeneities along the DNA) back to the
enzyme, destabilizing and knocking it off the DNA, or, they can be absorbed by
nearby lesions and guanine radicals. We develop a stochastic model to describe
the electron dynamics, and compute probabilities of electron capture by guanine
radicals and repair enzymes. We also calculate first passage times of electron
return, and ensemble-average these results over guanine radical distributions.
Our statistical results provide the rules that enable us to perform
implicit-electron Monte-Carlo simulations of repair enzyme binding and
redistribution near lesions. When lesions are electron absorbing, we show that
the CT mechanism suppresses wasteful buildup of enzymes along intact portions
of the DNA, maximizing enzyme concentration near lesions.
