User:BrianRatnasinghe/sandbox

Spore photoproduct lyase (, SAM, SP lyase, SPL, SplB, SplG) is a radical SAM enzyme that repairs DNA cross linking of thymine bases caused by UV-radiation. There are several types of thymine cross linking, but SPL specifically targets 5-thyminyl-5,6-dihydrothymine, which is also called spore photoproduct (SP). Spore photoproduct is the predominant type of thymine crosslinking in germinating endospores, which is why SPL is unique to organisms that produce endospores. Other types of thymine crosslinking, such as cyclobutane pyrimidine dimers (CPD) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs), are less commonly formed in endospores. These differences in DNA crosslinking are a function of differing DNA structure. Spore genomic DNA features many DNA binding proteins called small acid soluble proteins, which changes the DNA from the traditional B-form conformation to an A-from conformation. This difference in conformation is believed to be the reason why spores predominantly produce SP in response to UV-radiation.

The repair mechanism utilizing spore photoproduct lyase is one of the reasons for the resilience of certain bacterial spores. Through a series of radical reactions the photodimer, 3 5-thyminyl-5,6-dihydrothymine, is disconnected to give back two functional thymine rings. Spore photoproduct lyase is part of one of two main pathways which are used to repair cross linked 5-thyminyl-5,6-dihydrothymine caused by UV radiation: the spore-specific DNA repair system (which utilizes spore photoproduct lyase), and the general nucleotide excision repair pathway (NER).