PubMed · 681143
Iit is proposed that the family paramyxovirdae shall comprise three genera: paramyxovirus, Morbillivirus, and Pneumovirus.
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1978. Paramyxovirdae.. https://doi.org/10.1159/000148979
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Measles virus is a highly contagious virus that, despite the existence of an effective vaccine, is a major cause of illness and mortality worldwide. The virus has a negative-sense, single-stranded RNA genome that is encapsidated by the nucleocapsid protein (N) to form a helical ribonucleoprotein complex known as the nucleocapsid. This structure serves as the template for both transcription and replication. Paramyxovirus nucleocapsids are flexible structures, a trait that has hitherto hampered structural analysis even at low resolution. We have investigated the extent of this structural plasticity, using real-space methods to calculate three-dimensional reconstructions of recombinant nucleocapsids from cryo-negative stain transmission electron micrographs. Images of short sections of helix were sorted according to both pitch (the axial rise per turn) and twist (the number of subunits per turn). Our analysis indicates that there is extensive conformational flexibility within these structures, ranging in pitch from 50 Angstrom to 66 Angstrom, while twist varies from at least 13.04 to 13.44 with a greater number of helices comprising around 13.1 subunits per turn. We have also investigated the influence of the C terminus of N on helix conformation, analysing nucleocapsids after having removed this domain by trypsin digestion. We have found that this causes a marked change in both pitch and twist, such that the pitch becomes shorter, ranging from 46 Angstrom to 52 Angstrom, while more helices have a twist of approximately 13.3 subunits per turn. Our findings lead us to propose a mechanism whereby changes in conformation, influenced by interactions between viral or host proteins and the C terminus of N, might have a role in regulating the balance of transcription and replication during virus infection.
Complementary DNA clones of measles virus N, N (S228Q; L229D), Ncore (N1-400), Ntail (N401-525), P, PNT (P1-230), PCT (P231-507), L, MEL (L800-2183) and EL (L1300-2183) were fused in frame downstream of the Gal4 binding domain (BD) or activating domain (AD). All but BD-L, BD-MEL and BD-EL, were detected by western blot, with additional C- and/or N-terminal truncated products in the case of BD-N, and BD-P. BD-P and BD-PNT directly activated the reporter genes, indicating that the PNT domain displays transactivating properties. In yeast two-hybrid assays, PNT and PCT domains bind to Ncore and Ntail domains, respectively, indicating that N and P interact in a head to tail orientation via two independent binding sites. BD-N (S228Q; L229D) and AD-N displayed no or poor interaction with P proteins possibly because they may not be properly folded. L binding site on P lies within the PCT domain, and two PCT binding sites lie within the L1-799 and L800-1300 regions. Thus, N to P and P to L protein interactions in measles virus shared many features with other related Paramyxoviridae. From a human cDNA library, several candidate partners of N protein were identified which all reacted with BD-Ncore, and RNA was found to bridge the N protein with one partner.
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