The Sendai virus nucleocapsid exists in at least four different helical states

Abstract

Sendai virus nucleocapsids have been observed by electron microscopy to coexist in three different helical pitch conformations, 5.3, 6.8, and 37.5 nm. The 5.3and 6.8-nm conformations are present both in uranyl acetate negatively stained preparations and in tantalum-tungsten metal-shadowed preparations, whereas the 37.5-nm conformation, which has not been previously reported, is present only in the shadowed preparations. The 5.3-nm pitch conformation appears to be a mixture of two discrete structural states, with a small difference in the twist of the structure between the two. We have used image reconstruction techniques on an averaged data set from eight negatively stained nucleocapsids to produce a three-dimensional reconstruction at 2.4-nm resolution of the structure in one of the 5.3-nm pitch states. There are 13.07 nucleocapsid protein (NP) subunits in each turn of the helix in this state. The helical repeat is 79.5 nm, containing 196 subunits in 15 turns of the left-handed 5.3-nm helix. The arrangement of subunits produces a 5.0-nm-diameter hollow core which forms an internal helical groove. The RNA accounts for about 3% of the mass of the nucleocapsid, and so its location is not conspicuous in the reconstruction. Because the RNA remains associated with the NP subunits during mRNA transcription and genome replication, structural transitions in the nucleocapsid may determine the accessibility of the genome to polymerases. Alternatively, the large hollow core and internal helical groove we have reconstructed may allow access to the RNA even in the tightly coiled 5.3-nm pitch conformation.

Paramyxovirus mRNA editing leads to G deletions as well as insertions.

“…When a cDNA copy of a natural DI genome was expressed similarly to the synthetic DIs described here, except that the T7 transcript was the plus-strand antigenome strand, only viral genomes whose total length was a multiple of six were found to be amplified efficiently (Calain and Roux, 1993). This 'rule of six' is undoubtedly related to the fact that each NP monomer is associated with exactly six nucleotides (Egelman et al, 1989). This rule does not appear to apply to our system, in that we always expressed mRNAs regardless of whether the mini-genomes conformed to the rule of six (e.g.…”

Infectious Bursal Disease Virus: Ribonucleoprotein Complexes of a Double-Stranded RNA Virus

“…This ratio, calculated assuming that 100% of VP3 molecules are bound to dsRNA, is relatively low as compared with the nucleocapsid protein of the paramyxovirus Sendai virus, which is bound to six ribonucleotides. 37 We are also working on the functional analysis to determine at what ratio the RNP properties become evident. The appearance of the RNP of negativesense (e.g., filovirus, rhabdovirus, paramyxovirus, and orthomyxovirus) and positive-sense (e.g., coronaviruses) ssRNA viruses is highly variable, depending on salt concentration, deletion of specific C-or N-terminal regions, and/or the presence of specific ions.…”

Structure and Function of the C-terminal Domain of the Polymerase Cofactor of Rabies Virus

“…1 The vRNA of these viruses is bound to the viral nucleoprotein (N) with a virusfamily-specific nucleotide-N stoichiometry. [2][3][4][5] The viral RNA-dependent RNA polymerase consists of two subunits, the large protein (L) that contains the polymerase activity and a polymerase cofactor, the phosphoprotein (P) that binds L to the N-RNA. [6][7][8][9][10][11] The polymerase complex cannot transcribe or replicate the naked vRNA; vRNA has to be bound to N in order to be a functional template.…”