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Single Molecule Investigations of Impacts from Mycobacterial Topoisomerase I C-terminal Deletions on Supercoil Relaxation

Dillon Balthrop1, Deepesh Sigdel1, Chunfeng Mao1, Yuk-Ching Tse-Dinh2,3, and Maria Mills1,*

  • *Contact author: k.maria.mills@missouri.edu
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PRX Life 4, 033002 – Published 6 July, 2026

DOI: https://doi.org/10.1103/9tkx-w3zj

Abstract

Type IA topoisomerases relieve torsional stress in DNA by a strand-passage mechanism, using the strain in the DNA to drive relaxation. The topoisomerase IAs of the Mycobacterium genus have distinct C-terminal domains which are crucial for successful strand passage. We used single molecule magnetic tweezers to observe supercoil relaxation by wild type Mycobacterium smegmatis topoisomerase IA and two C-terminal truncation mutants. We recorded distinct behaviors from each truncation mutant. We calculated the free energy stored in the DNA as it is twisted under force to examine the differences between the proteins. Based on our results, we propose a modified model of the strand-passage cycle.

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References (41)

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PRX Life 4, 033002– Published 6 July, 2026
  • Received 29 October 2024
  • Accepted 11 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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