Dynamic Motions of the HIV-1 Frameshift Site RNA

The HIV-1 frameshift site (FS) plays a critical role in viral replication. During translation, the HIV-1 FS transitions from a 3-helix to a 2-helix junction RNA secondary structure. The 2-helix junction structure contains a GGA bulge, and purine-rich bulges are common motifs in RNA secondary structure. Here, we investigate the dynamics of the HIV-1 FS 2-helix junction RNA. Interhelical motions were studied under different ionic conditions using NMR order tensor analysis of residual dipolar couplings. In 150 mM potassium, the RNA adopts a 43°(±4°) interhelical bend angle (β) and displays large amplitude, anisotropic interhelical motions characterized by a 0.52(±0.04) internal generalized degree of order (GDO_int) and distinct order tensor asymmetries for its two helices (η = 0.26(±0.04) and 0.5(±0.1)). These motions are effectively quenched by addition of 2 mM magnesium (GDO_int = 0.87(±0.06)), which promotes a near-coaxial conformation (β = 15°(±6°)) of the two helices. Base stacking in the bulge was investigated using the fluorescent purine analog 2-aminopurine. These results indicate that magnesium stabilizes extrahelical conformations of the bulge nucleotides, thereby promoting coaxial stacking of helices. These results are highly similar to previous studies of the HIV transactivation response RNA, despite a complete lack of sequence similarity between the two RNAs. Thus, the conformational space of these RNAs is largely determined by the topology of their interhelical junctions.     

An integrative study of Necremnus Thomson (Hymenoptera: Eulophidae) associated with invasive pests in Europe and North America: taxonomic and ecological implications

The species of Necremnus attacking two invasive pests of tomato and canola in Europe and North America, respectively, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), have been revised using an integrative taxonomy approach. Molecular data from the mitochondrial cytochrome oxidase c subunit I and the nuclear D2 expansion region of the 28S ribosomal subunit and internal transcribed spacer 2, the discovery of new morphological features, and study of type material resulted in the delineation of three species groups, the Necremnus artynes, Necremnus cosconius, and Necremnus tidius groups, the discovery of four new species, and the resurrection of three taxa from synonymy. Lectotypes have been designated for 13 species originally described in Eulophus by Walker. Although Necremnus has not been revised, an illustrated key is given to differentiate 23 recognized European species. The key, type images, and treatments of the three species groups will enable more accurate identification of the valid species of Necremnus in the future. They will also benefit biological control practitioners of pest species. The ecological consequences of the new taxonomic concepts are discussed. © 2015 The Authors. Zoological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London