Translesion DNA synthesis across non-DNA segments in cultured human cells.
DNA lesions that have escaped DNA repair are tolerated via translesion DNA synthesis (TLS), carried out by specialized error-prone DNA polymerases. To evaluate the robustness of the TLS system in human cells, we examined its ability to cope with foreign non-DNA stretches of 3 or 12 methylene residues, using a gap-lesion plasmid assay system. We found that both the trimethylene and dodecamethylene inserts were bypassed with significant efficiencies in human cells, using both misinsertion and misalignment mechanisms. TLS across these non-DNA segments was aphidicolin-sensitive, and did not require poleta. In vitro primer extension assays showed that purified poleta, polkappa and poliota were each capable of inserting each of the four nucleotides opposite the trimethylene chain, but only poleta and polkappa could fully bypass it. Poleta and poliota, but not polkappa, could also insert each of the four nucleotides opposite the dodecamethylene chain, but all three polymerases were severely blocked by this lesion. The ability of TLS polymerases to insert nucleotides opposite a hydrocarbon chain, despite the lack of any similarity to DNA, suggests that they may act via a mode of transient and local template-independent polymerase activity, and highlights the robustness of the TLS system in human cells.
Adar
Sheera
S
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Livneh
Zvi
Z
D000818:Animals; D002478:Cells, Cultured; D003521:Cyclopropanes / Q000737:chemistry; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D006839:Hydrocarbons, Acyclic / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000378:metabolism; D013379:Substrate Specificity; D000094769:DNA Polymerase iota; D000099270:Y-Family DNA Polymerases
D003521:Cyclopropanes; D004247:DNA; D004259:DNA-Directed DNA Polymerase; D006839:Hydrocarbons, Acyclic; D009711:Nucleotides; D000094769:DNA Polymerase iota; C030797:cyclopropane; C404302:POLK protein, human; D000099270:Y-Family DNA Polymerases; C112338:Rad30 protein; C000722070:POLI protein, human