PICH and TOP3A cooperate to induce positive DNA supercoiling.

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Eukaryotic topoisomerases primarily relieve DNA torsional stress.
• Positive DNA supercoiling is hypothesized to be crucial for Topoisomerase 2a-mediated sister-chromatid disjunction during mitosis.

Purpose of the Study:

• To identify a eukaryotic enzymatic activity capable of introducing torsional stress into DNA.
• To elucidate the mechanism behind positive DNA supercoiling formation and its role in mitosis.

Main Methods:

• Investigated the enzymatic activities of human Plk1-interacting checkpoint helicase (PICH) and Topoisomerase 3a.
• Analyzed the formation of DNA supercoiling in vitro and in cellular contexts.

Main Results:

• Identified a novel eukaryotic enzymatic activity where PICH and Topoisomerase 3a collaborate to generate high-density positive DNA supercoiling.
• Demonstrated that PICH extrudes hypernegatively supercoiled DNA loops, which are then relaxed by Topoisomerase 3a, driving positive supercoil formation.
• This activity functions analogously to a reverse-gyrase.

Conclusions:

• The PICH-Topoisomerase 3a complex creates a positive supercoiling substrate.
• This positive supercoiling is proposed to optimize DNA for rapid sister centromere disjunction by Topoisomerase 2a at the start of anaphase.