Frequent meiotic recombination between the ends of truncated chromosome fragments of Saccharomyces cerevisiae

Clinical isolates of Candida auris with enhanced adherence and biofilm formation due to genomic amplification of ALS4

Candida auris is an emerging multidrug-resistant fungal pathogen and a new global threat to human health. A unique morphological feature of this fungus is its multicellular aggregating phenotype, which has been thought to be associated with defects in cell division. In this study, we report a new aggregating form of two clinical C. auris isolates with increased biofilm forming capacity due to enhanced adherence of adjacent cells and surfaces. Unlike the previously reported aggregating morphology, this new aggregating multicellular form of C. auris can become unicellular after treatment with proteinase K or trypsin. Genomic analysis demonstrated that amplification of the subtelomeric adhesin gene ALS4 is the reason behind the strain's enhanced adherence and biofilm forming capacities. Many clinical isolates of C. auris have variable copy numbers of ALS4, suggesting that this subtelomeric region exhibits instability. Global transcriptional profiling and quantitative real-time PCR assays indicated that genomic amplification of ALS4 results in a dramatic increase in overall levels of transcription. Compared to the previously characterized nonaggregative/yeast-form and aggregative-form strains of C. auris, this new Als4-mediated aggregative-form strain of C. auris displays several unique characteristics in terms of its biofilm formation, surface colonization, and virulence.

A Function for Subtelomeric DNA in Saccharomyces cerevisiae

The subtelomeric DNA sequences from chromosome I of Saccharomyces cerevisiae are shown to be inherently poor substrates for meiotic recombination. On the basis of these results and prior observations that crossovers near telomeres do not promote efficient meiosis I segregation, we suggest that subtelomeric sequences evolved to prevent recombination from occurring where it cannot promote efficient segregation.

Equal sister chromatid exchange is a major mechanism of double-strand break repair in yeast

Equal sister chromatid exchange (SCE) has been thought to be an important mechanism of double-strand break (DSB) repair in eukaryotes, but this has never been proven due to the difficulty of distinguishing SCE products from parental molecules. To evaluate the biological relevance of equal SCE in DSB repair and to understand the underlying molecular mechanism, we developed recombination substrates for the analysis of DSB repair by SCE in yeast. In these substrates, most breaks are limited to one chromatid, allowing the intact sister chromatid to serve as the repair template; both equal and unequal SCE can be detected. We show that equal SCE is a major mechanism of DSB repair, is Rad51 dependent, and is stimulated by Rad59 and Mre11. Our work provides a physical analysis of mitotically occurring SCE in vivo and opens new perspectives for the study and understanding of DSB repair in eukaryotes.

Inter-strain variability of insertion/deletion events in the Encephalitozoon cuniculi genome: a comparative KARD-PFGE analysis

We applied a two-dimensional pulsed-field gel electrophoresis procedure to the genomes of two karyotype variants assigned to two different strains of the microsporidian Encephalitozoon cuniculi, termed D (strain III) and F (strain II). Data obtained for BssHII and MluI restriction fragment length polymorphisms in each chromosome are compiled and compared to the reference strain I variant A. Six Insertion/Deletion (InDels) are found in subterminal position, some of these being characteristic of either D or F. Like in strain 1, the terminal fragments extending between each telomere and rDNA locus are conserved in length for each chromosome. They are however smaller than in reference variant. This size reduction is estimated to be 2.5 kbp for the strain III isolate and 3.5 kbp for the strain II isolate. We hypothesize that for the three E. cuniculi strains, all chromosome extremities are prone to a constant process of sequence homogenization through mitotic recombination between conserved regions.