Project description:Constitutive domains of repressive heterochromatin are maintained within the fission yeast genome through self-reinforcing mechanisms involving histone methylation and small RNAs. Non-coding RNAs generated from heterochromatic regions are processed into small RNAs by the RNA interference pathway, and are subject to silencing through both transcriptional and post-transcriptional mechanisms. While the pathways involved in maintenance of the repressive heterochromatin state are reasonably well understood, less is known about the requirements for its establishment. Here we describe a novel role for the post-transcriptional regulatory factor Mkt1 in establishment of heterochromatin at pericentromeres in fission yeast. Loss of Mkt1 does not affect maintenance of existing heterochromatin, but does affect its recovery following depletion, as well as de novo establishment of heterochromatin on a mini-chromosome. Pathway dissection revealed that Mkt1 is required for RNAi-mediated post-transcriptional silencing, downstream of small RNA production. Mkt1 physically associates with pericentromeric transcripts, and is additionally required for maintenance of silencing and heterochromatin at centromeres when transcriptional silencing is impaired. Our findings provide new insight into the mechanism of RNAi-mediated post-transcriptional silencing in fission yeast, and unveil an important role for post-transcriptional silencing in establishment of heterochromatin that is dispensable when full transcriptional silencing is imposed.
Project description:The low costs of array-synthesized oligonucleotide libraries are empowering rapid advances in quantitative and synthetic biology. Unfortunately, high synthesis error rates, uneven representation, and lack of access to individual oligonucleotides limit the true potential of these libraries. We have developed a cost-effective method called Recombinase Directed Indexing (REDI) to address these problems. The method involves integration of a complex library into yeast, site-specific recombination to index (i.e. barcode) library DNA, and then next-generation sequencing to identify clones containing the DNA of interest. We used REDI to generate a molecular probe library (n = ~3,300) that exhibited >96% purity and remarkable uniformity (>95% of probes were within 2-fold relative abundance of the median). Moreover, each sequence-verified probe was readily accessible. We also used REDI to rapidly create an arrayed collection of ~9,000 strains for CRISPR interference in yeast and demonstrate the utility of this collection for highly sensitive phenotypic screening. Our approach will enable a variety of applications requiring accurate, high-quality DNA libraries.
Project description:Global transcription machinery engineering (gTME) is an approach for reprogramming gene transcription to elicit cellular phenotypes important for technological applications. Here we show the application of gTME to Saccharomyces cerevisiae for improved glucose/ethanol tolerance, a key trait for many biofuels programs. Mutagenesis of the transcription factor Spt15p and selection led to dominant mutations that conferred increased tolerance and more efficient glucose conversion to ethanol. The desired phenotype results from the combined effect of three separate mutations in the SPT15 gene [serine substituted for phenylalanine (Phe177Ser) and, similarly, Tyr195His, and Lys218Arg]. Thus, gTME can provide a route to complex phenotypes that are not readily accessible by traditional methods. Keywords: stress response
Project description:The bacterium Bacillus subtilis is of high importance both as a model organism for Gram-positive bacteria and as an industrial work horse in the production of biomolecules. In recent years, advancements have been made to engineer the bacterium even further towards industrial applications. In this study, we present a novel screening method for mutant libraries using diamide, an oxidising agent that binds free thiols and creates disulfide bonds between them, thereby causing a so-called ‘disulfide stress’ in bacteria. The method shows promise to selectively identify phenotypes in B. subtilis with improved tolerance towards oxidative and disulfide-associated stress. Phenotypes initially identified by transposon mutagenesis were recreated through targeted gene deletions. Among the resulting deletion mutants, the largest difference in diamide tolerance compared to the parental strain was observed for pfkA and ribT deletion strains. A proteomics analysis showed that that diamide tolerance can be achieved through different routes involving increased expression of stress management proteins and reduced availability or activity of the RNA degradosome. We conclude that our screening method allows the facile identification of Bacillus strains with improved oxidative stress tolerance phenotypes
Project description:RNA interference (RNAi) is a gene-silencing pathway that can play roles in viral defense, transposon silencing, heterochromatin formation, and post-transcriptional gene silencing. Although absent from Saccharomyces cerevisiae, RNAi is present in other budding-yeast species, including Naumovozyma castellii, which have an unusual Dicer and a conventional Argonaute that are both required for gene silencing. To identify other factors that act in the budding-yeast pathway, we performed an unbiased genetic selection. This selection identified Xrn1p, the cytoplasmic 5′-to-3′ exoribonuclease, as a cofactor of RNAi in budding yeast. Deletion of XRN1 impaired gene silencing in N. castellii, and this impaired silencing was attributable to multiple functions of Xrn1p, including affecting the composition of siRNA species in the cell, influencing the efficiency of siRNA loading into Argonaute, degradation of cleaved passenger strand, and degradation of sliced target RNA.
Project description:RNA interference (RNAi) is a gene silencing mechanism conserved from fungi to mammals. Small interfering RNAs are products and mediators of the RNAi pathway and act as specificity factors in recruiting effector complexes. The Schizosaccharomyces pombe genome encodes one of each of the core RNAi proteins, Dicer, Argonaute and RNA-dependent RNA polymerase (dcr1, ago1, rdp1). Even though the function of RNAi in heterochromatin assembly in S. pombe is established, its role in controlling gene expression is elusive. Here, we report the identification of small RNAs mapped anti-sense to protein coding genes in fission yeast. We demonstrate that these genes are up-regulated at the protein level in RNAi mutants, while their mRNA levels are not significantly changed. We show that the repression by RNAi is not a result of heterochromatin formation. Thus, we conclude that RNAi is involved in post-transcriptional gene silencing in S. pombe.