The absence of the yeast chromatin assembly factor Asf1 increases genomic instability and sister chromatid exchange

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Abstract
Histone chaperone Asf1 participates in heterochromatin silencing, DNA repair and regulation of gene expression, and promotes the assembly of DNA into chromatin in vitro . To determine the influence of Asf1 on genetic stability, we have analysed the effect of asf1 Δ on homologous recombination. In accordance with a defect in nucleosome assembly, asf1 Δ leads to a loss of negative supercoiling in plasmids. Importantly, asf1 Δ increases spontaneous recombination between inverted DNA sequences. This increase correlates with an accumulation of double‐strand breaks (DSBs) as determined by immunodetection of phosphorylated histone H2A and fluorescent detection of Rad52–YFP foci during S and G2/M phases. In addition, asf1 Δ shows high levels of sister chromatid exchange (SCE) and is proficient in DSB‐induced SCE as determined by physical analysis. Our results suggest that defective chromatin assembly caused by asf1 Δ leads to DSBs that can be repaired by SCE, affecting genetic stability.