FIGURE 5-37 Formation of thymine-thymine dimers. (a) The most common type of DNA damage caused by UV irradiation is the formation of thymine-thymine dimers. (b) These lesions can be repaired by an excision-repair mechanism that recognizes the distortion they create in the shape of the DNA double helix. The red lines in (b) represent the UV-induced C—C bonds shown in (a).

[Part (b) data from K. McAteer et al., 1998, J Mol Biol. 282:1013, PDB ID 1ttd.]