TRF2 binds branched DNA to safeguard telomere integrity

Area of Science:

• * Molecular and Cellular Biology
• * Genetics and Genomics
• * DNA Repair Mechanisms

Background:

• * Telomeres, the protective caps of chromosomes, are structured as t-loops to prevent degradation.
• * T-loops can be converted into harmful Holliday junctions (HJs) by branch migration, risking telomere cleavage.
• * Holliday junction (HJ) resolvases pose a threat to t-loop integrity.

Purpose of the Study:

• * To investigate the role of the TRF2 basic domain in protecting telomeres from cleavage.
• * To elucidate the mechanism by which TRF2 represses t-loop cleavage.
• * To determine the in vivo significance of branched-DNA binding in telomere protection.

Main Methods:

• * In vitro binding assays of TRF2 basic domain and bacterial protein domains to three- and four-way DNA junctions.
• * In vivo experiments involving replacement of the TRF2 basic domain with alternative branched-DNA binding domains.
• * Analysis of t-loop cleavage in response to TRF2 basic domain deletion and BLM helicase activity.

Main Results:

• * The TRF2 basic domain binds to three- and four-way junctions, protecting HJs in vitro.
• * Replacing the TRF2 basic domain with bacterial domains confirmed the in vivo importance of branched-DNA binding.
• * Branched-DNA binding by TRF2 repressed PARP1 activity, a key factor in recruiting HJ resolvases.
• * BLM helicase-mediated removal of HJs mitigated t-loop cleavage upon loss of the TRF2 basic domain.

Conclusions:

• * TRF2's basic domain is crucial for masking and stabilizing the t-loop three-way junction.
• * This stabilization prevents the formation of potentially harmful Holliday junctions.
• * TRF2 activity protects telomeres from detrimental deletions and aberrant PARP1 activation.