Rescue of a Sendai virus DI genome by other parainfluenza viruses: implications for genome replication

Indiscriminate activities of different henipavirus polymerase complex proteins allow for efficient minigenome replication in hybrid systems

The henipaviruses, including Nipah virus (NiV) and Hendra virus (HeV), are biosafety level 4 (BSL-4) zoonotic pathogens that cause severe neurological and respiratory disease in humans. To study the replication machinery of these viruses, we developed robust minigenome systems that can be safely used in BSL-2 conditions. The nucleocapsid (N), phosphoprotein (P), and large protein (L) of henipaviruses are critical elements of their replication machinery and thus essential support components of the minigenome systems. Here, we tested the effects of diverse combinations of the replication support proteins on the replication capacity of the NiV and HeV minigenomes by exchanging the helper plasmids coding for these proteins among the two viruses. We demonstrate that all combinations including one or more heterologous proteins were capable of replicating both the NiV and HeV minigenomes. Sequence alignment showed identities of 92% for the N protein, 67% for P, and 87% for L. Notably, variations in amino acid residues were not concentrated in the N-P and P-L interacting regions implying that dissimilarities in amino acid composition among NiV and HeV polymerase complex proteins may not impact their interactions. The observed indiscriminate activity of NiV and HeV polymerase complex proteins is different from related viruses, which can support the replication of heterologous genomes only when the whole polymerase complex belongs to the same virus. This newly observed promiscuous property of the henipavirus polymerase complex proteins likely attributed to their conserved interaction regions could potentially be harnessed to develop universal anti-henipavirus antivirals.IMPORTANCEGiven the severity of disease induced by Hendra and Nipah viruses in humans and the continuous emergence of new henipaviruses as well as henipa-like viruses, it is necessary to conduct a more comprehensive investigation of the biology of henipaviruses and their interaction with the host. The replication of henipaviruses and the development of antiviral agents can be studied in systems that allow experiments to be performed under biosafety level 2 conditions. Here, we developed robust minigenome systems for the Nipah virus (NiV) and Hendra virus (HeV) that provide a convenient alternative for studying NiV and HeV replication. Using these systems, we demonstrate that any combination of the three polymerase complex proteins of NiV and HeV could effectively initiate the replication of both viral minigenomes, which suggests that the interaction regions of the polymerase complex proteins could be effective targets for universal and effective anti-henipavirus interventions.

RIG-I is required for VSV-induced cytokine production by murine glia and acts in combination with DAI to initiate responses to HSV-1

A defining feature of viral central nervous system (CNS) infection is the rapid onset of severe neuroinflammation. However, the mechanisms underlying glial responses to replicative neurotropic viruses are only now becoming apparent with the discovery of a number of cytosolic sensors for viral nucleic acids. We have described the expression by murine and human glial cells of two disparate pattern recognition receptors, retinoic acid inducible gene-I (RIG-I) and DNA-dependent activator of interferon regulatory factors (DAI), receptors for viral RNA and DNA moieties, respectively. In the present study, we demonstrate the functional significance of RIG-I expression in primary murine microglia and astrocytes. Our data indicate that murine glial immune responses to a model neurotropic RNA virus, vesicular stomatitis virus, are RIG-I dependent and independent of levels of DAI expression or RNA polymerase III activity. In contrast, maximal glial inflammatory and antiviral responses to the DNA virus herpes simplex virus-1 (HSV-1) are dependent on the expression of both RIG-I and DAI, and require RNA polymerase III activity. These findings indicate that the RNA sensor, RIG-I, acts in parallel with DAI in an RNA polymerase III-dependent manner to initiate glial responses to HSV-1. We therefore suggest that RIG-I plays a significant role in the detection of both RNA and DNA pathogens by microglia and astrocytes.

RIG-I mediates nonsegmented negative-sense RNA virus-induced inflammatory immune responses of primary human astrocytes

While astrocytes produce key inflammatory mediators following exposure to neurotropic nonsegmented negative-sense RNA viruses such as rabies virus and measles virus, the mechanisms by which resident central nervous system (CNS) cells perceive such viral challenges have not been defined. Recently, several cytosolic DExD/H box RNA helicases including retinoic acid-inducible gene I (RIG-I) have been described that function as intracellular sensors of replicative RNA viruses. Here, we demonstrate that primary human astrocytes constitutively express RIG-I and show that such expression is elevated following exposure to a model neurotropic RNA virus, vesicular stomatitis virus (VSV). Evidence for the functional nature of RIG-I expression in these cells comes from the observation that this molecule associates with its downstream effector molecule, interferon promoter stimulator-1, following VSV infection and from the finding that a specific ligand for RIG-I elicits astrocyte immune responses. Importantly, RIG-I knockdown significantly reduces inflammatory cytokine production by VSV-infected astrocytes and inhibits the production of soluble neurotoxic mediators by these cells. These findings directly implicate RIG-I in the initiation of inflammatory immune responses by human glial cells and provide a potential mechanism underlying the neuronal cell death associated with acute viral CNS infections.

Nucleocapsid structure and function

Measles virus belongs to the Paramyxoviridae family within the Mononegavirales order. Its nonsegmented, single-stranded, negative-sense RNA genome is encapsidated by the nucleoprotein (N) to form a helical nucleocapsid. This ribonucleoproteic complex is the substrate for both transcription and replication. The RNA-dependent RNA polymerase binds to the nucleocapsid template via its co-factor, the phosphoprotein (P). This chapter describes the main structural information available on the nucleoprotein, showing that it consists of a structured core (N(CORE)) and an intrinsically disordered C-terminal domain (N(TAIL)). We propose a model where the dynamic breaking and reforming of the interaction between N(TAIL) and P would allow the polymerase complex (L-P) to cartwheel on the nucleocapsid template. We also propose a model where the flexibility of the disordered N and P domains allows the formation of a tripartite complex (No-P-L) during replication, followed by the delivery of N monomers to the newly synthesized genomic RNA chain. Finally, the functional implications of structural disorder are also discussed in light of the ability of disordered regions to establish interactions with multiple partners, thus leading to multiple biological effects.

Structural disorder within the replicative complex of measles virus: functional implications

Measles virus belongs to the Paramyxoviridae family within the Mononegavirales order. Its non-segmented, single stranded, negative sense RNA genome is encapsidated by the nucleoprotein (N) to form a helical nucleocapsid. This ribonucleoproteic complex is the substrate for both transcription and replication. The RNA-dependent RNA polymerase binds to the nucleocapsid template via its co-factor, the phosphoprotein (P). In this review, we summarize the main experimental data pointing out the abundance of structural disorder within measles virus N and P. We also describe studies indicating that structural disorder is a widespread property in the replicative complex of Paramyxoviridae and, more generally, of Mononegavirales. The functional implications of structural disorder are also discussed. Finally, we propose a model where the flexibility of the disordered N and P domains allows the formation of a tripartite complex (N degrees-P-L) during replication, followed by the delivery of N monomers to the newly synthesized genomic RNA chain.

A reconstituted replication and transcription system for Ebola virus Reston and comparison with Ebola virus Zaire

The only known filovirus, which presumably is not pathogenic for humans, is Ebola virus (EBOV) Reston. When EBOV Reston and the highly pathogenic EBOV Zaire were grown in cell culture, comparison of the replication kinetics showed a clear growth impairment of EBOV Reston, indicating that the replication cycle of EBOV Reston might be delayed. In addition, the cytopathic effect caused by the virus was much milder with EBOV Reston than with EBOV Zaire. To compare replication and transcription of EBOV Reston and Zaire, a reconstituted minigenomic replication and transcription system based on reverse genetics has been established for EBOV Reston. This system was used to exchange the EBOV Zaire and EBOV Reston nucleocapsid (NC) proteins NP, VP35, VP30, and L, which catalyze replication and transcription. Furthermore, chimeric minigenomes were constructed containing the cis-acting replication signals of EBOV Zaire combined with those of EBOV Reston. Surprisingly, the cis-acting signals as well as almost all NC proteins could be exchanged between EBOV Reston and Zaire, suggesting a high degree of functional homology of the replication/transcription complexes of EBOV Zaire and EBOV Reston. Only the combination of EBOV Zaire VP35 and EBOV Reston L did not result in replication and transcription activity. Although these two proteins did not constitute an active polymerase complex, it was shown by immunofluorescence analysis that they were still able to interact.

Nipah virus conforms to the rule of six in a minigenome replication assay

To study the replication of Nipah virus (NiV), a minigenome replication assay that does not require the use of infectious virus was developed. The minigenome was constructed to encode a NiV vRNA analogue containing the gene for chloramphenicol acetyltransferase (CAT) under the control of putative NiV transcription motifs and flanked by the NiV genomic termini. CAT protein was detected only when plasmids encoding the NiV minigenome, nucleocapsid protein (N), phosphoprotein (P) and polymerase protein (L) were transfected into CV1 cells. To determine whether NiV conforms to the rule of six, a series of plasmids encoding minigenomes that differed in length by a single nucleotide was tested in the replication assay. CAT production was detected only with the minigenome whose length was an even multiple of six. The replication assay was also used to show that the N, P and L proteins of NiV recognize cis-acting sequences in the genomic termini of Hendra virus (HeV) but not measles virus. While these results suggest that NiV uses a replication strategy that is similar to those of other paramyxoviruses, they also support the inclusion of NiV and HeV in a separate genus within the subfamily Paramyxovirinae.

The L polymerase protein of parainfluenza virus 3 forms an oligomer and can interact with the heterologous Sendai virus L, P and C proteins

We recently showed that the L protein of Sendai virus is present as an oligomer in the active P-L polymerase complex [Smallwood et al., Virology 304 (2002) 235]. We now demonstrate using two different epitope tags that the L protein of a second respirovirus, human parainfluenza type 3 virus (PIV3), also forms an L-L complex. L oligomerization requires the coexpression of the differentially epitope tagged L proteins. By exploiting a series of C-terminal truncations the L-L binding site maps to the N-terminal half of L. There is some complex formation between the heterologous PIV3 and Sendai L and P proteins; however, the heterologous L protein does not function in transcription of either the PIV3 or Sendai template. The PIV3 C protein binds PIV3 L and inhibits RNA synthesis in vitro and in vivo. Significant homology exists between the C proteins of PIV3 and Sendai and complex formation occurs between the PIV3 and Sendai heterologous C and L proteins. In addition, the heterologous C proteins can inhibit transcription at approximately 50% of the level of the homologous protein. These data suggest that while the C proteins may be functionally somewhat interchangeable, the L and P proteins are specific for each virus.

The hemagglutinin of canine distemper virus determines tropism and cytopathogenicity

Canine distemper virus (CDV) and measles virus (MV) cause severe illnesses in their respective hosts. The viruses display a characteristic cytopathic effect by forming syncytia in susceptible cells. For CDV, the proficiency of syncytium formation varies among different strains and correlates with the degree of viral attenuation. In this study, we examined the determinants for the differential fusogenicity of the wild-type CDV isolate 5804Han89 (CDV(5804)), the small- and large-plaque-forming variants of the CDV vaccine strain Onderstepoort (CDV(OS) and CDV(OL), respectively), and the MV vaccine strain Edmonston B (MV(Edm)). The cotransfection of different combinations of fusion (F) and hemagglutinin (H) genes in Vero cells indicated that the H protein is the main determinant of fusion efficiency. To verify the significance of this observation in the viral context, a reverse genetic system to generate recombinant CDVs was established. This system is based on a plasmid containing the full-length antigenomic sequence of CDV(OS). The coding regions of the H proteins of all CDV strains and MV(Edm) were introduced into the CDV and MV genetic backgrounds, and recombinant viruses rCDV-H(5804), rCDV-H(OL), rCDV-H(Edm), rMV-H(5804), rMV-H(OL), and rMV-H(OS) were recovered. Thus, the H proteins of the two morbilliviruses are interchangeable and fully functional in a heterologous complex. This is in contrast with the glycoproteins of other members of the family Paramyxoviridae, which do not function efficiently with heterologous partners. The fusogenicity, growth characteristics, and tropism of the recombinant viruses were examined and compared with those of the parental strains. All these characteristics were found to be predominantly mediated by the H protein regardless of the viral backbone used.

Two regions of the P protein are required to be active with the L protein for human parainfluenza virus type 1 RNA polymerase activity

The paramyxovirus P protein is an essential component of the viral RNA polymerase composed of P and L proteins. In this study, we characterized the physical and functional interactions between P and L proteins using human parainfluenza virus type 1 (hPIV1) and its counterpart Sendai virus (SV). The hPIV1 P and SV L proteins or the SV P and hPIV1 L proteins formed complexes detected by anti-P antibodies. Functional analysis using the minigenome SV RNA containing CAT gene indicated that the hPIV1 P--SV L complex, but not the SV P--hPIV1 L complex, was biologically active. Mutant SV P or hPIV1 P cDNAs, which do not express C proteins, showed the same phenotype with wild-type P cDNAs, indicating that C proteins are not responsible for the dysfunction of SV P--hPIV1 L polymerase complex. Using the chimeric hPIV1/SV P cDNAs, we identified two regions (residues 387--423 and 511--568) on P protein, which are required for the functional interaction with hPIV1 L. These regions overlap with a previously identified domain for oligomer formation and binding to nucleocapsids. Our results indicate that in addition to a P--L binding domain, hPIV1 L requires a specific region on P protein to be biologically functional as a polymerase.

Establishment of a rescue system for canine distemper virus

Canine distemper virus (CDV) has been rescued from a full-length cDNA clone. Besides Measles virus (MV) and Rinderpest virus, a third morbillivirus is now available for genetic analysis using reverse genetics. A plasmid p(+)CDV was constructed by sequential cloning using the Onderstepoort vaccine strain large-plaque-forming variant. The presence of a T7 promoter allowed transcription of full-length antigenomic RNA by a T7 RNA polymerase, which was provided by a host range mutant of vaccinia virus (MVA-T7). Plasmids expressing the nucleocapsid protein, the phosphoprotein, and the viral RNA-dependent RNA polymerase, also under control of a T7 promoter, have been generated. Infection of HeLa cells with MVA-T7 and subsequent transfection of p(+)CDV plus the helper plasmids led to syncytium formation and release of infectious recombinant (r) CDV. Comparison of the rescued virus with the parental virus revealed no major differences in the progression of infection or in the shape and size of syncytia. A genetic tag, consisting of two nucleotide changes within the coding region of the L protein, has been identified in the rCDV genome. Expression by rCDV of all the major viral structural proteins has been demonstrated by immunofluorescence.

Comparison of the transcription and replication strategies of marburg virus and Ebola virus by using artificial replication systems

The members of the family Filoviridae, Marburg virus (MBGV) and Ebola virus (EBOV), are very similar in terms of morphology, genome organization, and protein composition. To compare the replication and transcription strategies of both viruses, an artificial replication system based on the vaccinia virus T7 expression system was established for EBOV. Specific transcription and replication of an artificial monocistronic minireplicon was demonstrated by reporter gene expression and detection of the transcribed and replicated RNA species. As it was shown previously for MBGV, three of the four EBOV nucleocapsid proteins, NP, VP35, and L, were essential and sufficient for replication. In contrast to MBGV, EBOV-specific transcription was dependent on the presence of the fourth nucleocapsid protein, VP30. When EBOV VP30 was replaced by MBGV VP30, EBOV-specific transcription was observed but with lower efficiency. Exchange of NP, VP35, and L between the two replication systems did not lead to detectable reporter gene expression. It was further observed that neither MBGV nor EBOV were able to replicate the heterologous minigenomes. A chimeric minigenome, however, containing the EBOV leader and the MBGV trailer was encapsidated, replicated, transcribed, and packaged by both viruses.

Nonsegmented negative-strand RNA viruses: genetics and manipulation of viral genomes

Protocols to recover negative-stand RNA viruses entirely from cDNA have been established in recent years, opening up this virus group to the detailed analysis of molecular genetics and virus biology. The unique gene-expression strategy of nonsegmented negative-strand RNA viruses, which involves replication of ribonucleoprotein complexes and sequential synthesis of free mRNAs, has also allowed the use of these viruses to express heterologous sequences. There are advantages in terms of easy manipulation of constructs, high capacity for foreign sequences, genetically stable expression, and the possibility of adjusting expression levels. Fascinating prospects for biomedical applications and transient gene therapy are offered by chimeric virus vectors carrying novel envelope protein genes and targeted to defined host cells.

Measles virus nucleocapsid protein can function in Sendai virus defective interfering particle genome synthesis in vitro

The Sendai virus P and L proteins, the viral RNA polymerase, and the nucleocapsid protein, NP, synthesized in a transient mammalian expression system support the replication of Sendai virus defective interfering particle (DI) genome RNA in vitro. We have shown that the measles virus nucleocapsid protein, N, can substitute for the Sendai NP protein in genome synthesis. The chimeric product nucleocapsids, which contained Sendai RNA encapsidated with measles N protein, were atypical since they were sensitive to micrococcal nuclease digestion, unlike wild-type Sendai or measles nucleocapsids. The utilization of measles N protein required the endogenous Sendai virus RNA polymerase, since DI nucleocapsids free of polymerase were not replicated. Although both Sendai virus NP and P proteins and measles N and P proteins formed complexes when they were coexpressed, sedimentation analysis showed that measles N protein self-assembled and did not form a complex when expressed with the Sendai P protein. Furthermore, when the Sendai P-L polymerase complex was provided separately, measles N protein alone synthesized DI genome RNA in the absence of Sendai P protein. These data suggest that the self-assembled form of measles N protein functions in Sendai DI genome synthesis.

Sequence and genome organization of Borna disease virus

We have previously demonstrated that Borna disease virus (BDV) has a negative nonsegmented single-stranded (NNS) RNA genome that replicates in the nucleus of infected cells. Here we report for the first time the cloning and complete sequence of the BDV genome. Our results revealed that BDV has a genomic organization similar to that of other members of the Mononegavirales order. We have identified five main open reading frames (ORFs). The largest ORF, V, is located closest to the 5' end in the BDV genome and, on the basis of strong homology with other NNS-RNA virus polymerases, is a member of the L-protein family. The intercistronic regions vary in length and nucleotide composition and contain putative transcriptional start and stop signals. BDV untranslated 3' and 5' RNA sequences resemble those of other NNS-RNA viruses. Using a set of overlapping probes across the BDV genome, we identified nine in vivo synthesized species of polyadenylated subgenomic RNAs complementary to the negative-strand RNA genome, including monocistronic transcripts corresponding to ORFs I, II, and IV, as well as six polycistronic polyadenylated BDV RNAs. Interestingly, although ORFs III and V were detected within polycistronic transcripts, their corresponding monocistronic transcripts were not detected. Our data indicate that BDV is a member of the Mononegavirales, specially related to the family Rhabdoviridae. However, in contrast to the rest of the NNS-RNA animal viruses, BDV replication and transcription occur in the nucleus of infected cells. These findings suggest a possible relationship between BDV and the plant rhabdoviruses, which also replicate and transcribe in the nucleus.

The rule of six, a basic feature for efficient replication of Sendai virus defective interfering RNA

The addition of the hepatitis delta virus genomic ribozyme to the 3' end sequence of a Sendai virus defective interfering RNA (DI-H4) allowed the reproducible and efficient replication of this RNA by the viral functions expressed from cloned genes when the DI RNA was synthesized from plasmid. Limited nucleotide additions or deletions (+7 to -7 nucleotides) in the DI RNA sequence were then made at five different sites, and the different RNA derivatives were tested for their abilities to replicate. Efficient replication was observed only when the total nucleotide number was conserved, regardless of the modifications, or when the addition of a total of 6 nucleotides was made. The replicated RNAs were shown to be properly enveloped into virus particles. It is concluded that, to form a proper template for efficient replication, the Sendai virus RNA must contain a total number of nucleotides which is a multiple of 6. This was interpreted as the need for the nucleocapsid protein to contact exactly 6 nucleotides.

Rescue of synthetic analogs of genomic RNA and replicative-intermediate RNA of human parainfluenza virus type 3

The genome of human parainfluenza virus type 3 (PIV3) is a single negative-sense RNA strand (vRNA) that is 15,463 nucleotides in length. A cDNA was constructed to encode an 898-nucleotide, internally deleted version of PIV3 vRNA, PIV3-CAT vRNA, in which the viral genes were replaced with the bacterial chloramphenicol acetyltransferase (CAT) reporter gene. The CAT gene was flanked in turn by sequences representing (i) nontranslated sequences of the first and last genes in the PIV3 genome, (ii) PIV3 gene-start and gene-end sequences, which are presumed to be transcription signals, and (iii) 3' extracistronic (leader) and 5' extracistronic (trailer) terminal regions of PIV3 vRNA. A second cDNA was constructed to encode the exact complement of PIV3-CAT vRNA; this positive-sense RNA, PIV3-CAT vcRNA, would correspond to the predicted replicative intermediate of PIV3-CAT vRNA. When synthesized in vitro by runoff transcription with T7 RNA polymerase and transfected separately into PIV3-infected cells, both PIV3-CAT vRNA and vcRNA were rescued with similar efficiencies; that is, they were expressed to yield CAT and were packaged into particles that could be used to infect fresh cells. Rescue of PIV3-CAT vRNA was strictly dependent on complementation by PIV3; PIV3 could not be replaced by respiratory syncytial virus or, unexpectedly, by a bovine strain of PIV3. Passage was blocked by prior incubation with neutralizing monoclonal antibodies specific to the PIV3 attachment protein. Also, during nine serial passages, the expression of CAT by PIV3-CAT vRNA increased more than 3,000-fold. These results indicated that the 3'-terminal 111 nucleotides and the 5'-terminal 115 nucleotides of PIV3 vRNA, which are present in PIV3-CAT vRNA, contained all of the cis-acting RNA sequences required for replication, gene expression, and transmission.

Loss of V protein expression in human parainfluenza virus type 1 is not a recent event

The P gene of paramyxoviruses usually contains an alternate overlapping ORF coding for a short cysteine-rich domain called V. This domain was thought to be a common feature of these genes as it is present in ten paramyxoviruses. However, the V ORF region of the P gene of one strain of human parainfluenza-virus type 1 (isolated in 1957) was recently found to be closed by no less than 9 stop codons. To determine whether the absence of the V ORF here might be due to the long adaptation of this strain in culture, 3 other more recent isolates were examined. Small differences in the V region were found, but all had conserved the vast majority of the stop codons. Moreover, examination of most of the intercistronic regions of the PIV1 genome failed to uncover a cryptic V gene. The V ORF is then unlikely to be a common feature of paramyxovirus P genes.

Subacute sclerosing panencephalitis virus dominantly interferes with replication of wild-type measles virus in a mixed infection: implication for viral persistence

Interaction between the Edmonston or Nagahata strain of acute measles virus (MV) and the defective Biken strain of MV isolated from a patient with subacute sclerosing panencephalitis (SSPE) was examined by a cell fusion protocol. Biken-CV-1 cells nonproductively infected with Biken strain SSPE virus were fused with neomycin-resistant CV-1 cells. All the fused cells selected with the neomycin analog G418 expressed Biken viral proteins, as determined by an immunofluorescence assay. This procedure enabled the transfer of Biken viral genomes into cells previously infected with MV. In the fused cells coinfected by Biken strain SSPE virus and Edmonston or Nagahata strain MV, early MV gene expression was suppressed, as determined by immunoprecipitation with strain-specific antibodies. Maturation of Edmonston strain MV was also suppressed. When the coinfected fused cells were selected with G418, Biken viral proteins remained at a constant level for up to 7 weeks. Wild-type MV proteins gradually decreased to a barely detectable level after 4 weeks and became undetectable after 7 weeks. Immunofluorescence studies showed a steady decline in cells expressing wild-type MV proteins in the coinfected cultures. These results suggest that Biken strain SSPE virus dominantly interferes with the replication of wild-type MV. The possible mechanisms of dominant interference and the implication for evolution of a persistent MV infection are discussed.

Tn9 CAT gene contains a promoter for vaccinia virus transcription: implications for reverse-genetic techniques

Vaccinia virus-dependent CAT expression was observed in virus-infected cells cotransfected with a promoterless CAT gene. Restriction endonuclease resection of the CAT plasmid indicated that expression was due to recognition by vaccinia virus RNA polymerase of sequences within the CAT gene itself, probably located within the 5' untranslated region of the gene. This observation is relevant to the design of reverse-genetic systems which use CAT as a reporter gene to detect replication of negative-strand RNA virus pseudogenomes.

Nucleotide sequences of the 3' leader and 5' trailer regions of human respiratory syncytial virus genomic RNA

The nucleotide sequences of the 3' extracistronic (leader) and 5' extracistronic (trailer) regions were determined for genomic RNA (vRNA) of human respiratory syncytial virus (RSV) strain A2. To sequence the 3' leader region, vRNA was extracted from purified virions, size-selected, polyadenylated, copied into cDNA, amplified by the polymerase chain reaction, cloned, and sequenced. The 3' leader sequence is 44 nt, which is somewhat shorter than its counterparts (50 to 70 nt) in other nonsegmented negative-strand viruses sequenced to date. The 5' trailer region was mapped and sequenced in part directly by dideoxynucleotide sequencing of vRNA. The sequence was confirmed and completed by analysis of cDNA clones derived from vRNA. The 5' trailer sequence is 155 nt in length, which is substantially longer than its counterparts (40 to 70 nt) in other nonsegmented negative-strand viruses. Ten of the 11 terminal nt of the 3' leader and 5' trailer regions were complementary. Among the other paramyxoviruses, the terminal 5 to 16 nt of the leader and trailer regions are highly conserved, but the corresponding RSV sequences were identical to the others only for the terminal 2 nt of each end. Surprisingly, the termini of the RSV leader and trailer regions were in somewhat better agreement with those of the rhabdoviruses vesicular stomatitis virus and rabies virus, sharing identity for the first 3 or 4 nt.

Characterization of the Sendai virus V protein with an anti-peptide antiserum

The Sendai virus V protein, which is a fusion of the P and V ORFs of the P gene, was characterized with antisera to a portion of the V ORF and compared to the P protein. The only property found in common with P is that V is also highly phosphorylated, and this is so even when these proteins are expressed independently of the other viral proteins. Otherwise, V was not found in virions, was not strongly associated with viral nucleocapsids like P, and anti-V had no effect on viral RNA synthesis in vitro under conditions where anti-P was highly inhibitory. The available evidence suggests that V may play a role in RNA synthesis, but it is not an essential one like that of the P protein.