Arrested replication forks guide retrotransposon integration.

Long terminal repeat (LTR) retrotransposons are an abundant class of genomic parasites that replicate by insertion of new copies into the host genome. Fungal LTR retrotransposons prevent mutagenic insertions through diverse targeting mechanisms that avoid coding sequences, but conserved principles guiding their target site selection have not been established. Here, we show that insertion of the fission yeast LTR retrotransposon Tf1 is guided by the DNA binding protein Sap1 and that the efficiency and location of the targeting depend on the activity of Sap1 as a replication fork barrier.

Implementation of the CRISPR-Cas9 system in fission yeast.

Application of the CRISPR-Cas9 genome editing system in the model organism Schizosaccharomyces pombe has been hampered by the lack of constructs to express RNA of arbitrary sequence. Here we present expression constructs that use the promoter/leader RNA of K RNA (rrk1) and a ribozyme to produce the targeting guide RNA. Together with constitutive expression of Cas9, this system achieves selection-free specific mutagenesis with efficiencies approaching 100%.