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The 63 kDa ' 63K ' movement protein encoded by the triple gene block of poa semilatent virus (PSLV) comprises the C-terminal NTPase/helicase domain and the N-terminal extension domain, which contains two positively charged sequence motifs, A and B. In this study, the in vitro RNAbinding properties of PSLV 63K and its mutants were analysed. Membrane-immobilized 63K and N-63K (isolated N-terminal extension domain) bound RNA at high NaCl concentrations. In contrast, C-63K (isolated NTPase/helicase domain) was able to bind RNA only at NaCl concentrations of up to 50 mM. In gel-shift assays, C-63K bound RNA to form complexes that were unable to enter an agarose gel, whereas complexes formed by N-63K could enter the gel. Full-length 63K formed both types of complexes. Visualization of the RNA-protein complexes formed by 63K, N-63K and C-63K by atomic force microscopy demonstrated that each complex had a different shape. Collectively, these data indicate that 63K has two distinct RNA-binding activities associated with the NTPase/helicase domain and the N-terminal extension domain. Mutations in either of the positively charged sequence motifs A and B had little effect on the RNA binding of the N-terminal extension domain, whereas mutations in both motifs together inhibited RNA binding. Hybrid viruses with mutations in motifs A and B were able to infect inoculated leaves of Nicotiana benthamiana plants, but were unable to move systemically to uninoculated leaves, suggesting that the RNA-binding activity of the N-terminal extension domain of PSLV 63K is associated with virus long-distance movement.

Two types of hexaglycylamide (HGA) epitaxial lamellar structures coexisting on the surface of highly oriented pyrolytic graphite (HOPG) exposed to water solutions were studied by high-resolution atomic force microscopy (AFM). Lamellae are distinguished by growth direction and by morphology. The lamellae of the first type (L1) produced by depositions from more dilute solutions are close-packed with a period of ∼5.2 nm, twice the HGA molecular length, and form highly ordered domains morphologically similar to the lamellar domains of alkanes. The less-ordered lamellae of the second type (L2) appear at intermediate and large HGA concentrations and demonstrate variable lamellar width, morphological diversity, and a tendency to merge. The interlamellar separation in the domains of close-packed L2 lamellae varies with the discrete increment ∼2.5 nm; the most frequently observed value is ∼7.5-8.0 nm corresponding to the triple HGA molecular length. The growth directions of lamellae of each type have sixfold rotational symmetry indicating epitaxy with graphite; however, the rosettes of L1 and L2 lamellae orientations are misaligned by 30°. The molecular modeling of possible HGA epitaxial packing arrangements on graphite and their classification have been conducted, and the energetically preferable structures are selected. On this basis, the structural models of the L1 and L2 lamellae are proposed explaining the experimentally observed peculiarities as follows: (1) the L1 and L2 lamellae are respectively parallel and antiparallel β-sheets with two HGA molecules in the unit cell oriented normally to the lamellae boundaries, (2) HGA molecules in L1 and L2 lamellae have different orientations with respect to the graphite lattice, respectively along the directions <1120> and <1010>, (3) L1 lamella is the assembly of two hydrogen-bonded parallel β-sheets oriented head-to-head, (4) L2 lamellae are assemblies of several molecular rows (antiparallel β-sheets) cross-linked by hydrogen bonds. The AFM observations indicate that the covering of the hydrophobic graphite by the dense, closely packed, well-ordered monolayers of hydrophilic oligopeptide is possible.

Magnetic properties of inhomogeneous nanoisland FeNi films were studied by SQUID magnetometry. The FeNi films with nominal thickness ranging from 0.6 to 2.0 nm were deposited by rf sputtering on Sitall glass substrates and covered by a protecting Al2O3 layer on the top. The SQUID data indicate pronounced irreversibility behavior for the out-of-plane temperature-dependent magnetization response (measured at H≃100 Oe) using zero-field cooling (ZFC) and field-cooled warming (FCW) after the applied dc magnetizing field Hm≃2 T for the FeNi samples with nominal thickness 1.1 nm ≲d≲1.8 nm, below the percolation threshold. The positive difference between the FCW and ZFC data identifies two irreversibility temperature scales, TB≈50 K and T⁎≈200 K, which can be associated with the superparamagnetic and superferromagnetic behavior in inhomogeneous nanoisland FeNi films, respectively. However, above the film percolation threshold, we observed a crossover from the out-of-plane to in-plane magnetization orientation. Here, the in-plane FCW-ZFC difference implies negative remanent magnetization response in the temperature range TB≲T≲T⁎. The observed magnetization properties can be associated with the presence of the superferromagnetic phase in self-assembled clusters of quasi-2D metallic magnetic FeNi nanoislands.

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