Homologous Recombination via Synthesis-Dependent Strand Annealing in Yeast Requires the Irc20 and Srs2 DNA Helicases

Author:

Miura Tohru1,Yamana Yoshimasa2,Usui Takehiko3,Ogawa Hiroaki I2,Yamamoto Masa-Toshi1,Kusano Kohji12

Affiliation:

1. Center for Genetic Resource Education and Development, Kyoto Institute of Technology, Kyoto 616-8354, Japan

2. Department of Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kita-Kyushu, 808-0196, Japan

3. Institute for Protein Research, Osaka University, Suita 565-0871, Japan

Abstract

Abstract Synthesis-dependent strand-annealing (SDSA)-mediated homologous recombination replaces the sequence around a DNA double-strand break (DSB) with a copy of a homologous DNA template, while maintaining the original configuration of the flanking regions. In somatic cells at the 4n stage, Holliday-junction-mediated homologous recombination and nonhomologous end joining (NHEJ) cause crossovers (CO) between homologous chromosomes and deletions, respectively, resulting in loss of heterozygosity (LOH) upon cell division. However, the SDSA pathway prevents DSB-induced LOH. We developed a novel yeast DSB-repair assay with two discontinuous templates, set on different chromosomes, to determine the genetic requirements for somatic SDSA and precise end joining. At first we used our in vivo assay to verify that the Srs2 helicase promotes SDSA and prevents imprecise end joining. Genetic analyses indicated that a new DNA/RNA helicase gene, IRC20, is in the SDSA pathway involving SRS2. An irc20 knockout inhibited both SDSA and CO and suppressed the srs2 knockout-induced crossover enhancement, the mre11 knockout-induced inhibition of SDSA, CO, and NHEJ, and the mre11-induced hypersensitivities to DNA scissions. We propose that Irc20 and Mre11 functionally interact in the early steps of DSB repair and that Srs2 acts on the D-loops to lead to SDSA and to prevent crossoverv.

Publisher

Oxford University Press (OUP)

Subject

Genetics

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