Y-family DNA polymerase iota (Pol ι) is involved in DNA damage response and tolerance. Mutations and altered expression level of POLI gene are linked to a higher incidence of cancer. We biochemically characterized five active site polymorphic variants of human Pol ι: R71G (rs3218778), P118L (rs554252419), I236M (rs3218784), E251K (rs3218783) and P365R (rs200852409). We analyzed fidelity of nucleotide incorporation on undamaged DNA, efficiency and accuracy of DNA damage bypass, as well as 5′-deoxyribophosphate lyase (dRP-lyase) activity. The I236M and P118L variants were indistinguishable from the wild-type Pol ι in activity. The E251K and P365R substitutions altered the spectrum of nucleotide incorporation opposite several undamaged DNA bases. The P365R variant also reduced the dRP-lyase activity and possessed the decreased TLS activity opposite 8-oxo-G. The R71G mutation dramatically affected the catalytic activities of Pol ι. The reduced DNA polymerase activity of the R71G variant correlated with an enhanced fidelity of nucleotide incorporation on undamaged DNA, altered lesion-bypass activity and reduced dRP-lyase activity. Therefore, this amino acid substitution likely alters Pol ι functions in vivo.
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Cover Image
In this issue, Lee and colleagues (pp. 1471–1484) demonstrate a new mechanism for tau secretion potentially involved in neurodegenerative disease progression, involving syntaxins (STX) 6 and 8. The cover image shows immunostaining of primary mouse neurons transfected with eGFP-STX6 (green) and human V5-tau (red) with co-localization of V5-tau and eGFP-STX6 in secretory vesicles. Superimposed is a schematic illustrating the proposed transmembrane transfer of tau via STX6/8 TM, STX6 or STX8 into the trans-Golgi network (TGN) or recycling endosomes (RE) for subsequent secretion. The cover image was provided by Lars M Ittner.
DNA Polymerase and dRP-lyase activities of polymorphic variants of human Pol ι
Evgeniy S. Shilkin, Anastasia S. Gromova, Margarita P. Smal, Alena V. Makarova; DNA Polymerase and dRP-lyase activities of polymorphic variants of human Pol ι. Biochem J 16 April 2021; 478 (7): 1399–1412. doi: https://doi.org/10.1042/BCJ20200491
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