Loss of Cohesin Subunit Rec8 Switches Rad51 Mediator Dependence in Resistance to Formaldehyde Toxicity in Ustilago maydis.

Jeanette H Sutherland,William K Holloman

doi:10.1534/genetics.118.301439

Abstract

DNA-protein cross-links (DPCs) are frequently occurring lesions that provoke continual threats to the integrity of the genome by interference with replication and transcription. Reactive aldehydes generated from endogenous metabolic processes or produced in the environment are sources that trigger cross-linking of DNA with associated proteins. DNA repair pathways in place for removing DPCs, or for bypassing them to enable completion of replication, include homologous recombination (HR) and replication fork remodeling (FR) systems. Here, we surveyed a set of mutants defective in known HR and FR components to determine their contribution toward maintaining resistance to chronic formaldehyde (FA) exposure in Ustilago maydis, a fungus that relies on the BRCA2-family member Brh2 as the principal Rad51 mediator in repair of DNA strand breaks. We found that, in addition to Brh2, Rad52 was also vital for resistance to FA. Deleting the gene for Rec8, a kleisin subunit of cohesin, eliminated the requirement for Brh2, but not Rad52, in FA resistance. The Rad51K133R mutant variant that is able to bind DNA but unable to dissociate from it was able to support resistance to FA. These findings suggest a model for DPC repair and tolerance that features a specialized role for Rad52, enabling Rad51 to access DNA in its noncanonical capacity of replication fork protection rather than DNA strand transfer.

Highlights

DNA–protein cross-links (DPCs) are frequently occurring lesions that provoke continual threats to the integrity of the genome by interference with replication and transcription
Processing of interstrand cross-links (ICLs) is associated with formation of DNA double-strand breaks (DSBs) at sites of stalled replication forks (Moldovan and D’Andrea 2009; Kottemann and Smogorzewska 2013), so it would be expected that the components of the canonical homologous recombination (HR) system would be brought into play to repair DNA damaged by exposure to diepoxybutane (DEB), which is a well-established bifunctional crosslinking reagent targeting DNA that is used as a diagnostic reagent in testing for Fanconi anemia (Auerbach 2015)
Resistance to FA toxicity in U. maydis depends on a set of HR and replication fork remodeling (FR) factors that includes Rad52 in addition to the primary Rad51 mediator Brh2

Summary

Introduction

DNA–protein cross-links (DPCs) are frequently occurring lesions that provoke continual threats to the integrity of the genome by interference with replication and transcription. From molecular and genetic studies performed in microbial as well as metazoan systems it has been found that different repair pathways converge to act in eliminating or tolerating DPCs induced by FA (de Graaf et al 2009; Ide et al 2011; Grogan and Jinks-Robertson 2012; Stingele and Jentsch 2015; Vaz et al 2017) These include the nucleotide excision repair (NER) pathway, DPC-targeted proteolysis (DPC-PR) coupled with translesion bypass synthesis, fork remodeling (FR), and the homologous recombination (HR) system. HR depends on a BRCA2 ortholog, which is not present in the mainstream yeast model systems (Kojic et al 2002), rather than Rad, and the nonhomologous endjoining Ku proteins are essential in human, contrary to findings in the mainstream yeasts (de Sena-Tomás et al 2015)

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Results

Conclusion