"Base Flipping": Photodamaged DNA-RNA Duplexes Are Poor Substrates for Photoreactivating DNA-Repair Enzymes.

What is damaged cannot always be readily repaired. This is observed for particular areas in the genome (mutation hot spots), which are repaired with low efficiency. DNA-DNA duplexes that exist in the B-conformation are repaired relatively efficiently by photolyases. DNA-RNA duplexes, which prefer an A-type conformation are only moderately destabilized by DNA photolesions and are slowly repaired. This suggests that the DNA conformation modulates the necessary "flipping" process for the repair of DNA lesions.