Oxidative DNA damage is important in aging and a variety of diseases. Significant advances have been made in our understanding of the chemistry of radical mediated DNA damage. These studies have been carried out on DNA in the absence of proteins. However, in cells DNA is typically bound by proteins such as in chromatin and transiently by proteins that regulate biochemical processes. How and whether protein binding affects DNA radical reactivity is not well understood, The effect of the DNA binding protein Hbb on the reactivity of the 5-(2'-deoxyuridinyl)methyl radical (1) and 5-(2'-deoxycytidinyl)methyl radical (2) was studied. Hbb bends DNA and disrupts base stacking at the sites of kinking. The reactivity of 1 and 2 are signficantly affected when they are generated at the kinking site in the presence of Hbb. The increased conformational mobility of the radicals results in significantly higher yields of DNA interstrand cross-links, These studies provide the first specific data on how protein binding affects the reactivity of a DNA radical and bring us closer to understanding oxidative DNA damage in cells.