Assembly and disassembly intermediates of maize streak geminivirus.

Maize streak virus (MSV) belongs to the Geminiviridae. Four forms of MSV coat protein (CP) assemblages were isolated from infected plants: geminate capsids, T = 1 icosahedral capsids, pentamers and decamers of CPs. Sequential exposure of geminate capsids to increasing pH, from 4.8 to 7.2 was used to monitor capsid disassembly. The capsids remain intact at pH4.8, disassemble to decamers and pentamers by pH6.4 and aggregate by pH7.2. Similarly, high salt and divalent cations cause disassembly. The disassembly process was reversed in low pH and low salt, but resulted in empty (no DNA) single and geminate capsid assemblies. This is likely due to disruption of CP-DNA interactions under acidic conditions and suggests a mechanism of capsid assembly in which the genome is packaged into preformed empty capsids. The pH assay developed in this study provides a method for characterizing the conditions that are the determinants of geminivirus assembly and disassembly.

Band gap expansion, shear inversion phase change behaviour and low-voltage induced crystal oscillation in low-dimensional tin selenide crystals.

In common with rocksalt-type alkali halide phases and also semiconductors such as GeTe and SnTe, SnSe forms all-surface two atom-thick low dimensional crystals when encapsulated within single walled nanotubes (SWNTs) with diameters below ∼1.4 nm. Whereas previous density functional theory (DFT) studies indicate that optimised low-dimensional trigonal HgTe changes from a semi-metal to a semi-conductor, low-dimensional SnSe crystals typically undergo band-gap expansion. In slightly wider diameter SWNTs (∼1.4-1.6 nm), we observe that three atom thick low dimensional SnSe crystals undergo a previously unobserved form of a shear inversion phase change resulting in two discrete strain states in a section of curved nanotube. Under low-voltage (i.e. 80-100 kV) imaging conditions in a transmission electron microscope, encapsulated SnSe crystals undergo longitudinal and rotational oscillations, possibly as a result of the increase in the inelastic scattering cross-section of the sample at those voltages.