Abstract
The clustered DNA lesions (CDLs) are a characteristic feature of ionizing radiation’s impact on the human genetic material. CDLs impair the efficiency of cellular repair machinery, especially base excision repair (BER). When CDLs contain a lesion repaired by BER (e.g., apurinic/apyrimidinic (AP) sites) and a bulkier 5′,8-cyclo-2′-deoxypurine (cdPu), which is not a substrate for BER, the repair efficiency of the first one may be affected. The cdPus’ influence on the efficiency of nuclear BER in xrs5 cells have been investigated using synthetic oligonucleotides with bi-stranded CDL (containing (5′S) 5′,8-cyclo-2′-deoxyadenosine (ScdA), (5′R) 5′,8-cyclo-2′-deoxyadenosine (RcdA), (5′S) 5′,8-cyclo-2′-deoxyguanosine (ScdG) or (5′R) 5′,8-cyclo-2′-deoxyguanosine (RcdG) in one strand and an AP site in the other strand at different interlesion distances). Here, for the first time, the impact of ScdG and RcdG was experimentally tested in the context of nuclear BER. This study shows that the presence of RcdA inhibits BER more than ScdA; however, ScdG decreases repair level more than RcdG. Moreover, AP sites located ≤10 base pairs to the cdPu on its 5′-end side were repaired less efficiently than AP sites located ≤10 base pairs on the 3′-end side of cdPu. The strand with an AP site placed opposite cdPu or one base in the 5′-end direction was not reconstituted for cdA nor cdG. CdPus affect the repair of the other lesion within the CDL. It may translate to a prolonged lifetime of unrepaired lesions leading to mutations and impaired cellular processes. Therefore, future research should focus on exploring this subject in more detail.
Highlights
Every living cell is constantly exposed to DNA damaging factors, e.g., reactive oxygen species (ROS), endogenous metabolites, replication errors, chemotherapeutics, ionizing radiation, etc
The experimental model was synthetic double-stranded oligonucleotides with dU in one strand and 50,8-cyclo-20 -deoxypurines in opposite strand: ScdA, RcdA, ScdG, and RcdG (Table 1)
Efficient 50 -32 P-end-labeling of single-stranded oligonucleotides and annealing to duplex was verified on native polyacrylamide gels (Figure S1)
Summary
Every living cell is constantly exposed to DNA damaging factors, e.g., reactive oxygen species (ROS), endogenous metabolites, replication errors, chemotherapeutics, ionizing radiation, etc. While NER removes bulky DNA damage (including 50 ,8-cyclo-20 -deoxypurines (cdPus)); the most common repair mechanism is BER. It corrects a single nucleotide lesion (short-patch BER, (SP–BER)) or a fragment of 2–12 nucleotides (long-patch BER, (LP–BER)) [4]. ExciMoreover, BER is theincludes most evolutionary conserved repair pathway in living organisms sion, filling a gap with the correct nucleotide (or fragment of nucleotide chain), and strand. CdPus affect the geometry of the DNA helix in the 5′ direction from from the lesion and inhibit the activity thesystem. In nucleosomal-bound DNA, the cleavage of two AP sites in sites in +1 position is reduced due to major structural changes needed in APE1 to incise. Tions in medicine, pharmacy, and food science [35]
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