No abstract

Several methods for ultra high-throughput DNA sequencing are currently under investigation. Many of these methods yield very short blocks of sequence information (reads). Here we report on an analysis showing the level of genome sequencing possible as a function of read length. It is shown that re-sequencing and de novo sequencing of the majority of a bacterial genome is possible with read lengths of 20–30 nt, and that reads of 50 nt can provide reconstructed contigs (a contiguous fragment of sequence data) of 1000 nt and greater that cover 80% of human chromosome 1.

Within the framework of the Peyrard-Bishop model for DNA melting, sharp denaturation temperature profiles can currently be obtained only if anharmonic base-pair stacking interactions are considered. We show that, when solvent interactions are included, a sharp denaturation of the DNA double helix is obtained without the need for anharmonic nearest-neighbor interactions. Using the concept of pseudo-Schrödinger equations we discuss the analogy of these transition to quantum-mechanical tunneling, and in particular we show that the sharp transitions are similar to resonant tunneling.

No abstract

Structural conversion of cellular prion protein (PrP C ) into scrapie PrP (PrP Sc ) and subsequent aggregation are key events associated with the onset of transmissible spongiform encephalopathies (TSEs). Experimental evidence supports the role of nucleic acids (NAs) in assisting this conversion. Here, we asked whether PrP undergoes liquid-liquid phase separation (LLPS) and if this process is modulated by NAs. To this end, two 25-mer DNA aptamers, A1 and A2, were selected against the globular domain of recombinant murine PrP (rPrP 90-231 ) using SELEX methodology. Multiparametric structural analysis of these aptamers revealed that A1 adopts a hairpin conformation. Aptamer binding caused partial unfolding of rPrP 90-231 and modulated its ability to undergo LLPS and fibrillate. In fact, although free rPrP phase separated into large droplets, aptamer binding increased the number of droplets but noticeably reduced their size. Strikingly, a modified A1 aptamer that does not adopt a hairpin structure induced formation of amyloid fibrils on the surface of the droplets. We show here that PrP undergoes LLPS, and that the PrP interaction with NAs modulates phase separation and promotes PrP fibrillation in a NA structure and concentration-dependent manner. These results shed new light on the roles of NAs in PrP misfolding and TSEs. |