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 RNA (rrk1) and a ribozyme to produce the targeting guide RNA. Tobether with constitutive expressio nof Cas9, this system achieves selection-free specific mutagenesis with efficiencies approaching 100%. The rrk1 CRISPR-Cas9 method enables rapid and efficient genome manipulation and unlocks the CRISPR toolset for use in fission yeast.

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. We propose that Sap1 and the fork arrest it causes guide insertion of Tf1 by tethering the integration complex to target sites.

ABSTRACTEndospore formation byBacillus subtilisis a complex and dynamic process. One of the major challenges of sporulation is the assembly of a protective, multilayered, proteinaceous spore coat, composed of at least 70 different proteins. Spore coat formation can be divided into two distinct stages. The first is the recruitment of proteins to the spore surface, dependent on the morphogenetic protein SpoIVA. The second step, known as encasement, involves the migration of the coat proteins around the circumference of the spore in successive waves, a process dependent on the morphogenetic protein SpoVID and the transcriptional regulation of individual coat genes. We provide genetic and biochemical evidence supporting the hypothesis that SpoVID promotes encasement of the spore by establishing direct protein-protein interactions with other coat morphogenetic proteins. It was previously demonstrated that SpoVID directly interacts with SpoIVA and the inner coat morphogenetic protein, SafA. Here, we show by yeast two-hybrid and pulldown assays that SpoVID also interacts directly with the outer coat morphogenetic protein, CotE. Furthermore, by mutational analysis, we identified a specific residue in the N-terminal domain of SpoVID that is essential for the interaction with CotE but dispensable for the interaction with SafA. We propose an updated model of coat assembly and spore encasement that incorporates several physical interactions between the principal coat morphogenetic proteins.

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