Yeast Pif1 Accelerates Annealing of Complementary DNA Strands

Pif1 is a helicase involved in the maintenance of nuclear and mitochondrial genomes in eukaryotes. Here we report a new activity of <i>Saccharomyces cerevisiae</i> Pif1, annealing of complementary DNA strands. We identified preferred substrates for annealing as those that generate a duplex product with a single-stranded overhang relative to a blunt end duplex. Importantly, we show that Pif1 can anneal DNA in the presence of ATP and Mg²⁺. Pif1-mediated annealing also occurs in the presence of single-stranded DNA binding proteins. Additionally, we show that partial duplex substrates with 3′-single-stranded overhangs such as those generated during double-strand break repair can be annealed by Pif1