The unique role of polymerase μ in nonhomologous end joining Public Deposited

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  • March 21, 2019
  • Davis, Bryan Joseph
    • Affiliation: School of Medicine, Department of Biochemistry and Biophysics
  • Nonhomologous end-joining (NEHJ) has the challenge of repairing DNA double strand breaks (DSBs) without using an intact template molecule to instruct synthesis. NHEJ solves this problem in part by recruiting polymerases from the pol X family to fill gaps that are present at some DSBs. If a gap has some complementary bases, multiple pol X family members can participate in NHEJ, but only pol μ is able to fill the gap if the DNA ends are noncomplementary. I determined that pol μ fills these gaps in a template-directed way, successfully using as template a DNA strand that is not annealed to the primer. My results show pol μ is able to do this because it interacts with DNA on both sides of the gap. Further, I demonstrate that the polymerase is most efficient when it participates in such an end-bridging complex. I then determined the roles of two amino acid residues in pol μ's activity on noncomplementary ends. As a similar residue does in TdT, H329 helps pol μ stabilize the incoming nucleotide when the template strand does not. However, unlike TdT, I show pol μ is not promiscuously template independent. I argue this is in part because pol μ also possesses an element of the more canonical template dependent pol X family members. R175 is part of the 8 kDa domain and helps position the template opposite the primer terminus through an interaction with the downstream phosphate. Pol μ is the only polymerase that has both of these elements and the combination confers the unique ability to fill gaps between noncomplementary ends.
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  • Ramsden, Dale
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  • University of North Carolina at Chapel Hill
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