Paramyxoviruses are a family of negative sense RNA viruses whose members cause serious diseases in humans, such as measles virus, mumps virus and respiratory syncytial virus; and in animals, such as Newcastle disease virus and rinderpest virus. Paramyxovirus particles form by assembly of the viral matrix protein, the ribonucleoprotein complex and the surface glycoproteins at the plasma membrane of infected cells and subsequent viral budding. Two major glycoproteins expressed on the viral envelope, the attachment protein and the fusion protein, promote attachment of the virus to host cells and subsequent virus-cell membrane fusion. Incorporation of the surface glycoproteins into infectious progeny particles requires coordinated interplay between the three viral structural components, driven primarily by the matrix protein. In this review, we discuss recent progress in understanding the contributions of the matrix protein and glycoproteins in driving paramyxovirus assembly and budding while focusing on the viral protein interactions underlying this process and the intracellular trafficking pathways for targeting viral components to assembly sites. Differences in the mechanisms of particle production among the different family members will be highlighted throughout.

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Published in Viruses, v. 6, no. 8, p. 3019-3054.

© 2014 by the authors; licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).

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We gratefully acknowledge support from NIAID/NIH grant R21AI108260 to R.E.D. and A.P.S., and NIH Grant #2P20 RR020171 from the National Center for Research Resources to R.E.D. We are also grateful to members of the Dutch lab for critical review of the manuscript.

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Figure 1.

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Figure 2. (A) Schematic of a paramyxovirus particle. The viral envelope, containing two main surface glycoproteins: fusion protein (purple) and attachment protein (magenta), surrounds the single stranded RNA genome (gray) which is encapsidated by the nucleocapsid protein (brown) and bound by phosphoprotein (orange) and the large polymerase protein (yellow). Underlying the membrane is a layer of matrix proteins (green). (B) Schematic illustration of the life cycle of paramyxoviruses. Transcription and replication of the viral genome occurs in the cytoplasm by the action of the viral RNA-dependent RNA polymerase. The newly synthesized viral components translocate to discrete sites at the infected cell plasma membrane where assembly and budding of infectious virus particles occur. For details, refer to text.

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Figure 3. Conserved domain structures of paramyxovirus fusion protein (A) and attachment protein (B). Abbreviation: fusion peptide (FP); heptad repeat region (HRA, HRB); transmembrane domain (TMD); cytoplasmic tail (CT); disulfide bond (S-S).

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Figure 4. Amino acid sequences of the cytoplasmic tails of the fusion protein (A) and attachment protein (B) of different paramyxoviruses. Amino acid residues highlighted contribute to paramyxovirus particle production. Sequences of cytoplasmic tails were obtained from UniProt.

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Figure 5. Potential models of paramyxovirus assembly: fusion protein shown in purple, attachment protein in magenta, matrix protein in green and the RNP complex in brown.