Flaviviruses have imperfect icosahedral symmetry

Flaviviruses assemble initially in an immature, noninfectious state and undergo extensive conformational rearrangements to generate mature virus. Previous cryo-electron microscopy (cryo-EM) structural studies of flaviviruses assumed icosahedral symmetry and showed the concentric organization of the external glycoprotein shell, the lipid membrane, and the internal nucleocapsid core. We show here that when icosahedral symmetry constraints were excluded in calculating the cryo-EM reconstruction of an immature flavivirus, the nucleocapsid core was positioned asymmetrically with respect to the glycoprotein shell. The core was positioned closer to the lipid membrane at the proximal pole, and at the distal pole, the outer glycoprotein spikes and inner membrane leaflet were either perturbed or missing. In contrast, in the asymmetric reconstruction of a mature flavivirus, the core was positioned concentric with the glycoprotein shell. The deviations from icosahedral symmetry demonstrated that the core and glycoproteins have varied interactions, which likely promotes viral assembly and budding.

Ediacaran fossils from the Innerelv Member (late Proterozoic) of the Tanafjorden area, northeastern Finnmark

An Ediacaran assemblage dominated by an unidentified species ofCyclomedusaSprigg 1947, along with species ofEdiacaria?Sprigg 1947,BeltanellaSprigg 1947,HiemaloraFedonkin 1982, andNimbia?Fedonkin 1980, is described for the first time from the Innerelv Member of the Stappogiedde Formation exposed in coastal outcrops west of Tanafjorden on Digermul Peninsula, in northeastern Finnmark, northern Norway. The fossil assemblage is dominated by discoidal forms which share certain affinities with the cosmopolitan genera.CyclomedusaandEdiacaria. However, our specimens differ from these and other discoidal Ediacaran fossils in the absence of radial sculpture. This, along with a basically concentric organization, are characteristics shared withKullingiafrom the Dividal Group of northern Scandinavia, the White Sea, Podolia, and northwestern Canada, along with undescribed discoidal remains from the Charnian Supergroup, Charnwood Forest, Leicestershire, England, and the Conception Group, Avalon Peninsula, Newfoundland.Our discovery of an Ediacaran-type assemblage within the Middle Innerelv Member provides support for previous suggestions of a late Vendian age for this sequence. This general conclusion is consistent with the occurrence of early Cambrian taxa, including the trace fossilPhycodes, and the problematical formsVendotaeniaandSabellidites,in basal portions of the Lower Breivik Formation, within the same stratigraphie section. The lowest formally-proposed faunal zone in northern Scandinavia is theKullingiaZone, based on the occurrence of the fossil medusoidKullingia concentricain Member III (Middle Sandstone C) of the Dividal Group, northern Scandinavia.Kullingiais a distinctly chambered form that was probably pelagic. In contrast,Cyclomedusa,and related genera of the so-calledCyclomedusaplexus, comprise an informal grouping of intergrading, probably benthic, taxa that possess radial and/or concentric organization. In light of the intergradational nature of taxa, present difficulties in taxonomic interpretation and correlation, and the abundance of cyclomedusoids in many Ediacaran assemblages, we suggest that the concept of theKullingiaZone, as originally defined for northern Scandanavia, be broadened to include the common form genera of theCyclomedusaplexus, inclusive of the occurrences in the Innerelv Member described herein. It is our hope that additional fieldwork will provide a basis for more refined taxonomic evaluations and biozonation.

Musical Evidence of Compositional Planning in the Renaissance: Josquin's Plus nulz regretz

While much discussed and analyzed, Josquin's setting of Plus nulz regretz mimics the structural features of the poem in ways which have gone undetected for two reasons: essential stylistic details of the "Chant nouvel" by Jean Lemaire de Belges have not been identified, and Josquin disguised his musical realization of those details. By first examining the text and comparing it to Lemaire's other surviving "Chant nouvel," and then analyzing the motivic organization of the chanson, the article shows that for every poetic gesture Josquin devised a musical counterpart, chief among which is a concentric organization of motives (ABCCBA) to match the rhyme scheme. The hypothesis that Josquin used techniques related to Leon Battista Alberti's methods for determining perspective in art is invoked to explain a striking symmetrical structure of temporal units. This in turn has implications for the way composers throughout the Renaissance planned proportional compositional structures.