The conserved SEN1 DNA/RNA helicase has multiple functions during yeast meiosis.

dnaRNA hybrids are unusual structures found throughout the genomes of many species, including yeast and mammals. While DNA:RNA hybrids may promote various cellular functions, persistent hybrids lead to double strand breaks, resulting in genomic instability. DNA:RNA hybrid formation and removal are therefore highly regulated, including by enzymes that either degrade or unwind RNA from the hybrid. Meiosis is the specialized cell division that creates haploid gametes for sexual reproduction. Previous work in yeast and mammals showed that elimination of DNA:RNA hybrids by RNase H facilitates meiotic recombination. This work demonstrates that the conserved Sen1 DNA/RNA helicase functions during three temporally distinct processes during yeast meiosis. First, SEN1 allows meiosis-specific genes to be expressed at the proper time to allow entry into meiosis. Second, SEN1 prevents the accumulation of hybrids during premeiotic DNA replication. Third, SEN1 promotes the repair of programmed meiotic double strand breaks that are necessary to form crossovers between homologous chromosomes to allow their proper segregation at the first meiotic division. Given the evolutionary conservation of Sen1 with its mammalian counterpart, Senataxin, studies of Sen1 function in yeast are likely to be informative about the regulation of DNA:RNA hybrids during human meiosis as well.