No abstract

Background:The helicase RHAU requires an N-terminal extension to bind quadruplex structures. Results: This extension adopts an elongated shape and interacts with the guanine tetrad face of quadruplexes. Conclusion: We provide a basis for the understanding of quadruplex binding by the N-terminal domain. Significance: The N-terminal region does not require the 2Ј-OH of the ribose to mediate the protein-quadruplex interaction.

No abstract

The identification of four-stranded G-quadruplexes (G4s) has highlighted the fact that DNA has additional spatial organisations at its disposal other than double-stranded helices. Recently, it became clear that the formation of G4s is not limited to the traditional G3+NL1G3+NL2G3+NL3G3+ sequence motif. Instead, the G3 triplets can be interrupted by deoxythymidylate (DNA) or uridylate (RNA) where the base forms a bulge that loops out from the G-quadruplex core. Here, we report the first high-resolution X-ray structure of a unique unimolecular DNA G4 with a cytosine bulge. The G4 forms a dimer that is stacked via its 5′-tetrads. Analytical ultracentrifugation, static light scattering and small angle X-ray scattering confirmed that the G4 adapts a predominantly dimeric structure in solution. We provide a comprehensive comparison of previously published G4 structures containing bulges and report a special γ torsion angle range preferentially populated by the G4 core guanylates adjacent to bulges. Since the penalty for introducing bulges appears to be negligible, it should be possible to functionalize G4s by introducing artificial or modified nucleotides at such positions. The presence of the bulge alters the surface of the DNA, providing an opportunity to develop drugs that can specifically target individual G4s.

Now you see it, now you don't: A specially designed reactor that heats only a small area of Pd foil during a Suzuki–Miyaura coupling permits observation of the surface changes during the reaction. Dissolution of Pd occurs only in the heated zone, and only in the presence of aryl iodide, whereas deposition of Pd occurs preferentially on the unheated zones adjacent to the reactive zone. SEM and XPS are employed to probe the surface before and after reaction.