Respiratory syncytial virus matrix protein associates with nucleocapsids in infected cells

Abstract

Little is known about the functions of the matrix (M) protein of respiratory syncytial virus (RSV). By analogy with other negative-strand RNA viruses, the M protein should inhibit the viral polymerase prior to packaging and facilitate virion assembly. In this study, localization of the RSV M protein in infected cells and its association with the RSV nucleocapsid complex was investigated. RSV-infected cells were shown to contain characteristic cytoplasmic inclusions. Further analysis showed that these inclusions were localization sites of the M protein as well as the N, P, L and M2-1 proteins described previously. The M protein co-purified with viral ribonucleoproteins (RNPs) from RSVinfected cells. The transcriptase activity of purified RNPs was enhanced by treatment with antibodies to the M protein in a dose-dependent manner. These data suggest that the M protein is associated with RSV nucleocapsids and, like the matrix proteins of other negative-strand RNA viruses, can inhibit virus transcription.Human respiratory syncytial virus (RSV) is a non-segmented negative-strand RNA virus belonging to the family Paramyxoviridae, genus Pneumovirus (Collins et al., 1996). RSVinfected cells contain characteristic cytoplasmic inclusions. Previous studies have shown that these inclusions contain the nucleocapsid (N) protein, the viral polymerase (P and L proteins) (Collins et al., 1996) and the transcription elongation factor protein M2-1 (Garcia et al., 1993). It has been proposed that, as with Sendai virus, the P protein interacts with the newly synthesized N protein to prevent incorrect assembly of the nucleocapsid and to deliver it to the nascent RNA during genome replication (Curran et al., 1995 ;Garcia-Barreno et al., 1996), whereas the M2-1 protein is required for the synthesis of full-length viral RNA (Collins et al., 1996). These obser-

The Human Respiratory Syncytial Virus Matrix Protein Is Required for Maturation of Viral Filaments

“…In HRSV-infected cells, the M protein is first detected in the cytoplasm and nucleus (19). The purpose of nuclear targeting is not well understood but may be to inhibit host cell transcription or to temporarily divert M away from sites of viral transcription, which it was shown to inhibit (18,21). At later times, M is increasingly detected in virus-induced IBs (18,21,35).…”

“…M is a nonglycosylated phosphorylated protein of 256 amino acids and a structural component of the HRSV virion (19,27,52). M is thought, in part by analogy to the role of matrix proteins in other virus systems, to play a key role in virion assembly by inhibiting viral transcription and by forming a bridge between the viral ribonucleoprotein (RNP) and envelope (13,21,25,27,54,56). However, the roles of HRSV M in virion assembly have not been well characterized.…”

High-throughput screening of stabilizers for Respiratory Syncytial Virus: Identification of stabilizers and their effects on the conformational thermostability of viral particles

“…8 Another important structural protein is the matrix protein (M) which is presumably the most abundant protein within the virion playing an important role in virus assembly through multiple interactions with cellular membranes, the F and G envelope proteins and the nucleocapsid. 9,10 The nucleocapsid is a helical structure formed by the single-strand RNA which is tightly bound to the nucleocapsid (N) protein. This structure together with the phosphoprotein (P) and the large polymerase (L) are the critical components for viral RNA replication.…”

Structure and assembly of a paramyxovirus matrix protein

“…These structures are built of one or two domains that have similar β-sandwich folds, suggesting gene duplication during evolution. The dimers of paramyxovirus M protein (approximately 40 kDa) can form a grid-like array on the inner surface of the viral membrane (15)(16)(17)(18), and probably interact with both the cytoplasmic tails of the HN and F glycoproteins (19,20) as well as the nucleocapsid (21)(22)(23)(24) to initiate virus assembly and budding (20). The NDV M protein has greater than 20% sequence identity with other paramyxovirus M proteins including measles, mumps, and the parainfluenza viruses.…”