A mechanism for the extension and unfolding of parallel telomeric G-quadruplexes by human telomerase at single-molecule resolution.

Telomeric G-quadruplexes (G4) were long believed to form a protective structure at telomeres, preventing their extension by the ribonucleoprotein telomerase. Contrary to this belief, we have previously demonstrated that parallel-stranded conformations of telomeric G4 can be extended by human and ciliate telomerase. However, a mechanistic understanding of the interaction of telomerase with structured DNA remained elusive. Here, we use single-molecule fluorescence resonance energy transfer (smFRET) microscopy and bulk-phase enzymology to propose a mechanism for the resolution and extension of parallel G4 by telomerase. Binding is initiated by the RNA template of telomerase interacting with the G-quadruplex; nucleotide addition then proceeds to the end of the RNA template. It is only through the large conformational change of translocation following synthesis that the G-quadruplex structure is completely unfolded to a linear product. Surprisingly, parallel G4 stabilization with either small molecule ligands or by chemical modification does not always inhibit G4 unfolding and extension by telomerase. These data reveal that telomerase is a parallel G-quadruplex resolvase.

Comparison of cellulose nanofiber properties produced from different parts of the oil palm tree.

Cellulose nanofibers (CNFs) were obtained from three types of oil palm wastes, mesocarp, empty fruit bunch (EFB), and palm kernel shell (PKS), as well as the trunk of the oil palm tree, to compare their morphological, thermal, and mechanical properties. Despite large differences in the chemical components of cell walls in the raw materials, the production of CNFs from all parts of the oil palm were achieved in this work. The morphology and mechanical properties of the CNF sheets obtained from the trunk had advantages over the CNF sheets from wastes, while the thermal degradation properties showed no advantage. Cellulose crystallinity of the CNF sheet from the mesocarp and PKS had lower crystallinity (69.1 and 71.1%), and the highest crystallinity of 77.0% was exhibited by the sheet from the trunk. The value of specific tensile strength and specific Young's modulus were highest in the CNF sheet of the trunk, and lowest mechanical properties shown in the CNF sheet from the mesocarp. These results strongly suggested that the CNF could be obtained from all parts of the plants, but their properties may vary.