Nucleases Specific for Ultraviolet Light-Irradiated DNA and their Possible Role in Dark Repair

Abstract

Bacteria are able to repair ultraviolet light (UV)-induced damage to their DNA in the absence of visible light. This process is called dark repair, and it has been established that some of these processes are of an enzymatic nature. Boyce and Howard-Flanders (1964), Setlow and Carrier (1964), and Pettijohn and Hanawalt (1964) postulated that these processes may proceed as illustrated in Fig. 1: (1) a single-strand fragment containing photoproducts such as thymine dimers is released from the UV-irradiated DNA; (2) new nucleotides complementary to those of the intact opposite strand are inserted into the gap so formed; and (3) the phosphodiester link is finally closed between the ‘new’ and ‘old’ nucleotides to reproduce the original double-stranded DNA. Although the precise mechanism of these reactions is still obscure, it is assumed that the second and third steps may be catalyzed by DNA polymerase and ligase respectively. However, enzymes which might be...