Telomerase RNA (TR) carries the template for synthesis of telomere DNA and provides a scaffold for telomerase assembly. Fungal TRs are long and have been compared to higher eukaryotes, where they show considerable diversity within phylogenetically close groups. TRs of several Saccharomycetaceae were recently identified, however, many of these remained uncharacterised in the template region. Here we show that this is mainly due to high variability in telomere sequence. We predicted the telomere sequences using Tandem Repeats Finder and then we identified corresponding putative template regions in TR candidates. Remarkably long telomere units and the corresponding putative TRs were found in Tetrapisispora species. Notably, variable lengths of the annealing sequence of the template region (1-10 nt) were found. Consequently, species with the same telomere sequence may not harbour identical TR templates. Thus, TR sequence alone can be used to predict a template region and telomere sequence, but not to determine these exactly. A conserved feature of telomere sequences, tracts of adjacent Gs, led us to test the propensity of individual telomere sequences to form G4. The results show highly diverse values of G4-propensity, indicating the lack of ubiquitous conservation of this feature across Saccharomycetaceae.

• MeSH
• Benzothiazoles metabolism   MeSH
• Fluorescence MeSH
• G-Quadruplexes MeSH
• Genetic Variation * MeSH
• Templates, Genetic * MeSH
• Reproducibility of Results MeSH
• RNA genetics   MeSH
• Saccharomycetales genetics   MeSH
• Base Sequence MeSH
• Telomerase genetics   MeSH
• Telomere genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Benzothiazoles MeSH
• RNA MeSH
• Telomerase MeSH
• telomerase RNA MeSH Browser
• thioflavin T MeSH Browser

We recently showed that Saccharomyces cerevisiae telomeric DNA can fold into an unprecedented pseudocircular G-hairpin (PGH) structure. However, the formation of PGHs in the context of extended sequences, which is a prerequisite for their function in vivo and their applications in biotechnology, has not been elucidated. Here, we show that despite its 'circular' nature, PGHs tolerate single-stranded (ss) protrusions. High-resolution NMR structure of a novel member of PGH family reveals the atomistic details on a junction between ssDNA and PGH unit. Identification of new sequences capable of folding into one of the two forms of PGH helped in defining minimal sequence requirements for their formation. Our time-resolved NMR data indicate a possibility that PGHs fold via a complex kinetic partitioning mechanism and suggests the existence of K+ ion-dependent PGH folding intermediates. The data not only provide an explanation of cation-type-dependent formation of PGHs, but also explain the unusually large hysteresis between PGH melting and annealing noted in our previous study. Our findings have important implications for DNA biology and nanotechnology. Overrepresentation of sequences able to form PGHs in the evolutionary-conserved regions of the human genome implies their functionally important biological role(s).

• MeSH
• Nucleic Acid Conformation MeSH
• DNA, Circular chemistry   MeSH
• Models, Molecular MeSH
• Nuclear Magnetic Resonance, Biomolecular MeSH
• Nucleotide Motifs MeSH
• Base Pairing MeSH
• Saccharomyces cerevisiae genetics   MeSH
• Stereoisomerism MeSH
• Telomere chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, Circular MeSH