Lesions containing site-specific

These studies used randomly damaged DNA and could not distinguish between inhibition of repair in the nucleosome core or linker DNA. More recent studies have used the in vitro assembly of nucleosomes containing site-specific DNA lesions within the core particle and either purified repair factors or mammalian cell extracts to examine in more detail the effect of chromatin structure on excision repair. It was determined that UV-induced photolesions as well as AAF- and cisplatin-modified bases located in nucleosome cores are repaired at a 5- to 10-fold reduced rate relative to the same lesions within the same sequence context in naked DNA (Hara and Sancar, 2002, 2003 Hara et al., 2000 Wang et aL, 2003). 

For a given lesion, error-free or error-prone synthesis by a bypass polymerase is often determined by in vitro translesion synthesis assays (Figure 22.21). The assay involves in vitro DNA synthesis by a purified bypass polymerase from an oligonucleotide template containing a site-specific lesion. A DNA primer labeled with 32P at its 5 end is annealed to the damaged template prior to assembling the assay reactions. Following the polymerase reaction, products are separated by electrophoresis... 

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