Department of Pathology, The University of Georgia, 501 D. W. Brooks Drive, Athens, GA 30602, USA
Correspondence
Zhen F. Fu
zhenfu{at}vet.uga.edu
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Present address: University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Present address: Center for Disease Control and Prevention, Atlanta, GA 30333, USA.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
RV N is phosphorylated (Sokol & Clark, 1973) at serine 389 (Dietzschold et al., 1987
) by casein kinase II (Wu et al., 2003
). N phosphorylation has been reported to play a modulatory role in the process of viral RNA transcription and replication since mutation of the phosphorylated serine in N leads to a reduction in viral transcription and replication (Wu et al., 2002
). Because unphosphorylated N binds more strongly to RNA than phosphorylated N (Yang et al., 1999
), we proposed that N phosphorylation plays a role in the process of viral RNA transcription and replication via modulation of RNA encapsidation. It has also been reported that phosphorylated N is detected in nucleocapsids, but not in the NP complex or as free N (Kawai et al., 1999
). This indicates that newly synthesized N is not immediately phosphorylated but rather is associated first with P, which suggests that RV N phosphorylation occurs during the processes of or after RNA encapsidation.
In the present study, we investigated RV N, P and RNA interactions in vivo by expressing these components either individually or in combination in insect and mammalian cells. Our results showed that when RV N was expressed alone, it could bind to any RNA, particularly the N mRNA. When N and P were co-expressed in vivo, the N and P formed NP complexes that did not bind to non-specific RNA. In the presence of RV (mini-)genomic RNA, the NP complex bound to genomic RNA. Furthermore, the N in the NP complex was not phosphorylated prior to encapsidation of the genomic RNA, suggesting that RV P, by binding to N, prevents phosphorylation of N.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Protein expression in insect cells.
Insect cells were infected with BRN, BRP or both as described previously (Fu et al., 1991, 1994
). At 8 days post-infection, cells were harvested and disrupted in a Dounce homogenizer. After removing nuclei and cell debris by centrifugation, supernatants were used to purify N or NRNA complexes.
Protein expression in mammalian cells.
Transfection and labelling of BSR cells were performed as described by Wu et al. (2002). Briefly, cells were infected with recombinant vaccinia virus. One hour later, cells were transfected with pRN alone, pRN and pRP, pRN and pRP plus pSDI-CAT, or pRN and pSDI-CAT. Alternatively, pRN was replaced by pRN-SA in the transfection. Twelve hours after transfection, cells were washed with PBS and incubated with methionine-free medium for 1 h. Cells were then labelled with [35S]methionine (Amersham) for 8 h. Cells were harvested and processed as above.
Purification of viral RNP, recombinant N and B-RNP.
Viral RNP was purified as described previously (Schneider et al., 1973). Cells infected with RV strain L16 were lysed with deionized H2O. After removing the cell debris and nuclei, supernatants were mixed with CsCl to a final concentration of 40 % (w/v) and centrifuged in an SW41 rotor at 37 000 r.p.m. overnight. The viral RNP band was collected and dialysed. Recombinant N was purified from insect cells by affinity chromatography as described (Fu et al., 1991
). The RNP-like structure from baculovirus-expressed N (B-RNP) was purified the same way as for viral RNP by mixing the affinity-purified N with CsCl.
Separation of NP complexes from NRNA or NPRNA complexes.
To separate further the N, P and NP complexes from NRNA complexes, discontinuous CsCl gradient centrifugation was performed as described previously (Spehner et al., 1997). Briefly, protein samples prepared from insect or mammalian cells were loaded on to a discontinuous CsCl gradient [2040 % (w/v)] in NTE buffer (0·2 M NaCl, 10 mM Tris/HCl, pH 8·0, 0·1 mM EDTA). After centrifugation in an SW41 rotor at 37 000 r.p.m. overnight, the gradient was fractionated from top to bottom into 18 fractions. Each of the fractions was dialysed against NTE buffer before use.
In vitro RNA encapsidation and gel-shift assay.
RV leader RNA was transcribed and labelled as described previously (Yang et al., 1998). RNA encapsidation was performed as follows: recombinant RV N or B-RNP was allowed to react with in vitro-transcribed RV leader RNA (106 c.p.m. per reaction). The RNAprotein mixtures were subjected to digestion with micrococcal nuclease and RNase A at 37 °C for 30 min. The products were analysed by electrophoresis on a 4 % polyacrylamide gel containing 5 % glycerol.
SDS-PAGE, Western blotting and immunoprecipitation.
Dialysed samples were subjected to electrophoresis on a 12 % polyacrylamide/10 % SDS gel and the separated proteins were electroblotted on to nitrocellulose membrane and incubated with anti-N or anti-P antibodies. After incubation with biotinylated secondary antibody, the proteins on the membrane were detected with DAB substrate (Vector Lab). For immunoprecipitation, samples were incubated with anti-N or anti-P antibodies overnight at 4 °C. Protein ASepharose was then added and the reaction incubated for 2 h at 4 °C. Immune complexes were precipitated, washed three times in NTE buffer and analysed by SDS-PAGE.
RNA extraction, Northern blotting and dot-blot hybridization.
RNA extraction was performed either from purified viral RNP, B-RNP, baculovirus-expressed N (B-N), different fractions of the CsCl gradient or from immunoprecipitated preparations using Trizol. RNA samples were subjected to electrophoresis and blotted on to membrane for Northern hybridization. Alternatively, RNA was directly dot blotted on to nylon membrane and fixed by UV cross-linking. Genomic RNA, a genomic analogue or N mRNA was detected by hybridization with digoxigenin-labelled N- or CAT-specific probes as described previously (Wu et al., 2002).
Phosphorylation of RV N protein.
To study the status of N phosphorylation, BSR cells were labelled with [32P]phosphoric acid (Amersham) as described previously (Wu et al., 2002). Cells were harvested and subjected to immunoprecipitation with anti-N antibodies followed by SDS-PAGE.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
To analyse whether recombinant N expressed in insect cells existed in forms other than the NRNA complex, we collected nine fractions from the cushion. An aliquot from each of the fractions (fractions 58 contained B-RNP) was analysed by SDS-PAGE followed by Coomassie blue staining. As shown in Fig. 1(a), N was found in every fraction. To analyse the RNA content, the B-RNP portion and the rest of the cushion (fractions 14) were pooled and RNA was extracted and subjected to electrophoresis. As shown in Fig. 1(c)
, many RNA species were observed ranging from approximately 100800 nt in the B-RNP portion (lane 2), but very little RNA was observed in the other fractions (lane 3). These data indicated that, although N was purified to near homogeneity by affinity chromatography (Fu et al., 1991
), both RNA-free N (approx. 40 %) and RNA-bound N (B-RNP, approx. 60 %) were found.
|
|
|
RV P confers the specificity of genomic RNA encapsidation in vivo
To investigate whether the NP complex confers specificity of encapsidation of genomic RNA, we employed the RV minigenomic system. BSR cells were transfected with pRN alone or in combination with pRP. Alternatively, RV N alone or N and P were expressed together with the minigenomic RNA (pSDI-CAT). As shown in Fig. 4(a), the N and P profiles in BSR cells transfected with pRN or pRN plus pRP were similar to those in insect cells expressing N and N plus P, respectively. Most of the N in cells expressing N alone was detected in the bottom fractions 1618. In contrast, most of the N in cells expressing both N and P shifted to the upper fractions 615. A minor portion of N was detected in the bottom fractions 1617; however, very little or no P was detected in the bottom fractions. In cells expressing N, P and the minigenomic RNA, the majority of N was detected in the bottom fractions 1618 and P was clearly detectable in these fractions as well. Thus, the protein profiles in cells expressing N, P and genomic RNA showed similar patterns to those in cells infected with RV (see Fig. 3a
). To investigate whether the ratio of N : P affected the NP interaction, we used an N : P ratio of either 10 : 1 or 1 : 10 with or without minigenomic RNA. However, similar protein profiles were observed (data not shown) regardless of the N : P ratio, indicating that the N : P ratio does not affect the NP or NPRNA interactions.
|
RV P, by binding to N, prevents N from being phosphorylated
To investigate whether N phosphorylation was involved in the RNA encapsidation process, we studied the phosphorylation status of N. As shown in Fig. 5, phosphorylated N was only detected in the bottom fractions 1618 from either infected or transfected cells. In cells expressing N and P, very little phosphorylated N was detected and very little N was found in the bottom fractions as shown in Fig. 4(a)
. N in the top fractions, where it is bound to P (Fig. 3a
), was not phosphorylated (Fig. 5
). These data indicated that RV N (mostly in NP complexes) was not phosphorylated before RNA encapsidation. It was phosphorylated either during or after RNA encapsidation. These results suggested that P, by binding to N, prevented N from being phosphorylated.
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Different methods have been used to purify RV N expressed in insect cells (Fu et al., 1991; Iseni et al., 1998
; Prehaud et al., 1990
). Using antibody affinity chromatography, we purified N to near homogeneity (Fu et al., 1991
) and this purified N was capable of interacting with P (Fu et al., 1994
) and binding RNA in vitro (Yang et al., 1998
). Using glycerol gradient sedimentation velocity centrifugation, Iseni et al. (1998)
purified N and found that the recombinant N formed ring-like structures. Further analysis (Iseni et al., 1998
; Schoehn et al., 2001
) indicated that these ring-like structures contained 911 N monomers, which encapsidated RNA of 8090 nt. In the present study, we also found that recombinant N encapsidated low-molecular-mass RNA. All these studies indicate that RV N encapsidates RNA and forms nucleocapsid-like structures (termed B-RNP in this study) in insect cells. These studies also raised the question of how recombinant N purified by antibody affinity chromatography (Fu et al., 1991
) was still capable of encapsidating RNA in vitro (Iseni et al., 1998
; Yang et al., 1998
). To address this, we further analysed N by centrifugation in 40 % CsCl and found that recombinant N expressed in insect cells existed as both RNA-free and RNA-bound forms. In vitro encapsidation assays revealed that the ability of RNA-bound N (B-RNP) to encapsidate in vitro-synthesized RNA decreased 15-fold when compared with RNA-free N (B-N). These results indicated that recombinant N in the B-RNP was no longer capable of encapsidating RNA. The RNA-binding activity of the affinity-purified N (Yang et al., 1998
) was not due to the removal of RNA from the B-RNP by alkaline pH during the purification process as suggested by Iseni et al. (1998)
. Rather, a portion of N purified by affinity chromatography exists as RNA-free N and thus is capable of encapsidating in vitro-synthesized RNA.
By sequencing some of the RNA associated with the recombinant N, Iseni et al. (1998) identified cellular tRNA, suggesting that RV N expressed in insect cells encapsidated cellular RNA. However, our in vitro encapsidation assay showed that RV N bound more strongly to N mRNA than to non-specific and non-viral RNA (Yang et al., 1998
). It could thus be assumed that, in insect cells, RV N would encapsidate N mRNA as well as other RNA species. To this end, we prepared RNA samples from B-RNP or nucleocapsid-like structures in mammalian cells for Northern blot hybridization using an N-specific probe. It was found that all the RNA samples hybridized with the N-specific probe, indicating that RV N encapsidated N mRNA in addition to cellular tRNA. Green et al. (2000)
also detected N mRNA encapsidated by VSV N when it was expressed in prokaryotes, further indicating that rhabdovirus N is capable of encapsidating N mRNA when expressed alone.
RV P, as in other negative-strand RNA viruses, plays multiple roles in the virus replication cycle. In addition to being the co-factor for RdRp, P interacts with N (Banerjee & Chattopadhyay, 1990; Wertz et al., 1987
). The NP interaction has many facets in the process of viral transcription and replication. P, by binding to N, not only keeps N soluble for RNA encapsidation (Banerjee & Chattopadhyay, 1990
; Wertz et al., 1987
) but also confers the specific encapsidation of genomic RNA (Banerjee et al., 1989
). Previous in vitro studies have amply demonstrated the latter function of P (Banerjee et al., 1989
; Wertz et al., 1987
; Yang et al., 1998
). However, few in vivo studies have been carried out to confirm these in vitro studies. In one report, Spehner et al. (1997)
expressed measles virus N and P either individually or in combination using recombinant vaccinia virus. They reported similar findings to those observed for RV N and P in the present paper. When N was expressed alone, most bound to non-specific RNA and formed nucleocapsid-like structures. When N was co-expressed with P, it interacted with P to form NP complexes that prevented N from encapsidating non-specific RNA. However, Spehner et al. (1997)
did not express genomic RNA in the system. When we expressed N, P and minigenomic RNA together, we observed that the NP complexes preferentially encapsidated the minigenomic RNA. All these data demonstrate that, although N by itself is capable of encapsidating any RNA species to form nucleocapsid-like structures, P, by binding to N, eliminates the encapsidation of non-specific RNA. A small amount of N and RNA was always detected in the bottom fractions in cells expressing N and P. This could be due to some of the N that has not yet formed a complex with P and is thus still capable of binding to non-specific RNA. Furthermore, non-specific binding of N RNA was also detected in cells expressing N, P and minigenomic RNA. This was also due to the fact that not all of N bound to P immediately after synthesis and thus a portion of the free N bound to non-specific RNA. This condition not only exists in cells expressing N, P and minigenomic RNA, but also in virus-infected cells. Binding of mRNA by N has been reported in RV-infected cells as mRNP (Wunner, 1991
). Together these results confirm previous in vitro findings that P, by binding to N, confers specific encapsidation of genomic RNA by eliminating non-specific RNA encapsidation (Yang et al., 1998
).
In addition to the functions reported previously, we found another function for P, at least in the RV model. RV P, by binding to N, prevents N from becoming phosphorylated. RV N is phosphorylated in virus-infected cells (Sokol & Clark, 1973), as well as when N is expressed alone in eukaryotic cells (Prehaud et al., 1990
; Yang et al., 1999
). N phosphorylation has been reported to play a modulatory role in the process of RV transcription and replication (Wu et al., 2002
; Yang et al., 1999
). Since unphosphorylated or dephosphorylated N binds to RNA more strongly than phosphorylated N, we assumed that RV N phosphorylation may be involved in the RNA encapsidation process. In the present study, we examined the phosphorylation status of RV N in virus-infected cells, as well as in cells expressing N alone, N and P, or N and P plus the minigenome. We found that N was not phosphorylated before RNA encapsidation and only RNA-bound N was phosphorylated. These findings are in agreement with the report by Kawai et al. (1999)
that phosphorylated N is detected only in the nucleocapsid, but not in the NP complex or as RNA-free N. Together, these studies indicate that N is phosphorylated either during or immediately after RNA encapsidation. The fact that only RNA-bound N was phosphorylated suggests that N phosphorylation per se is not important in the process of RNA encapsidation. However, these data suggest that P, by binding to N, prevents N from being phosphorylated.
Previously, we showed that unphosphorylated N had a higher affinity for RNA than phosphorylated N (Yang et al., 1999). Thus, it is advantageous for N not to be phosphorylated before encapsidating RNA. Here, we have shown definitively that RV N is not phosphorylated before RNA encapsidation, regardless of whether N is expressed alone or in virus-infected cells. During or after RNA encapsidation, N may go through conformational changes that enable it to be phosphorylated. We have hypothesized that, following phosphorylation, the charge repulsion between the negatively charged phosphoserine of N and the negatively charged genomic RNA may weaken the interaction between N and RNA, thus facilitating the initiation of the next round of viral RNA transcription and replication (Wu et al., 2002
). Recently, Toriumi & Kawai (2004)
reported that N phosphorylation enhances NP interactions in the nucleocapsid. Thus, although N phosphorylation may not be important in the RNA encapsidation process, it plays a role in subsequent replication cycles.
Another interpretation for the fact that N is not phosphorylated in NP complexes may be that RV N in NP complexes prior to RNA encapsidation is in a unique conformation. In such a conformation, N cannot be phosphorylated. Furthermore, we hypothesize that in such a unique conformation N can only encapsidate genomic RNA. However, the mechanisms by which P, by binding to N, keeps N in a unique conformation for specific encapsidation of genomic RNA are not clear. Recently, it has been shown that the N : P ratio in the NP complex before RNA encapsidation is 1 : 2 (Mavrakis et al., 2003). However, it has been reported that the N : P ratio is 2 : 1 in the purified virions (Wunner, 1991
). These observations suggest that the mode of NP interaction before RNA encapsidation is different from that after RNA encapsidation.
Based on all the available data, we propose the following model (Fig. 7) to explain the detailed N, P and RNA interactions and N phosphorylation. When N is expressed alone, it binds to any RNA (Fig. 7a
). During the process of NRNA interaction, the RNA-bound N undergoes a conformational change and becomes phosphorylated. When N is co-expressed with P, P binds N to form the NP complex, which eliminates non-specific RNA encapsidation. Because no RNA has been encapsidated, N has not undergone any conformational change and thus stays unphosphorylated (Fig. 7b
). When N, P and genomic RNA are expressed together, N can encapsidate genomic RNA and thus becomes phosphorylated (Fig. 7c
). Although the mechanisms by which RV N and P interact with each other to eliminate the binding of non-specific RNA are not understood, we offer the following explanations. It is possible that P binds to N and keeps N in a unique conformation. Due to steric hindrance, in such a conformation N cannot encapsidate non-specific RNA, but can still encapsidate genomic RNA. Because N is in such a conformation, it cannot be phosphorylated. Alternatively, RV P and RNA may share the same binding site. Due to some unknown characteristics, the genomic RNA, but not non-specific RNA, can displace P, thus encapsidating the genomic RNA. Because the phosphorylation site (aa 389) is close to the putative RNA-binding domain (aa 289352) (Kouznetzoff et al., 1998
), at this particular site, P might prevent N from phosphorylation. After displacing P and encapsidating RNA, N undergoes a conformational change, and thus becomes phosphorylated. Clearly, further studies are needed to investigate the dynamic interactions between N and P during the RNA encapsidation process, which could shed light on the mechanisms by which P, by binding to N, keeps N in the unique conformation that is able to encapsidate the genomic RNA.
|
![]() |
ACKNOWLEDGEMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Banerjee, A. K., Masters, P. S., Das, T. & Chattopadhyay, D. (1989). Specific interaction of vesicular stomatitis virus nucleocapsid protein (N) with the phosphoprotein (NS) prevents its binding with non-specific RNA. In Genetics and Pathogenicity of Negative Strand Viruses, pp. 121128. Edited by D. Kolakofsky & B. Mahy. Amsterdam: Elsevier.
Blumberg, B. M., Giorgi, C. & Kolakofsky, D. (1983). N protein of vesicular stomatitis virus selectively encapsidates leader RNA in vitro. Cell 32, 559567.[Medline]
Conzelmann, K.-K. & Schnell, M. (1994). Rescue of synthetic genomic RNA analogs of rabies virus by plasmid-encoded proteins. J Virol 68, 713719.[Abstract]
Dietzschold, B., Lafon, M., Wang, H., Otvos, L., Jr, Celis, E., Wunner, W. H. & Koprowski, H. (1987). Localization and immunological characterization of antigenic domains of rabies virus internal N and NS proteins. Virus Res 8, 103125.[CrossRef][Medline]
Fu, Z. F., Dietzschold, B., Schumacher, C. L., Wunner, W. H., Ertl, H. C. J. & Koprowski, H. (1991). Rabies virus nucleoprotein expressed in and purified from insect cells is efficacious as a vaccine. Proc Natl Acad Sci U S A 88, 20012005.[Abstract]
Fu, Z. F., Zheng, Y. M., Wunner, W. H., Koprowski, H. & Dietzschold, B. (1994). Both the N- and C-terminal domains of the nominal phosphoprotein of rabies virus are involved in binding to the nucleoprotein. Virology 200, 590597.[CrossRef][Medline]
Fuerst, T. R., Niles, E. G., Studier, F. W. & Moss, B. (1986). Eukaryotic transient-expression system based on recombinant vaccinia virus that synthesizes bacteriophage T7 RNA polymerase. Proc Natl Acad Sci U S A 83, 81228126.[Abstract]
Green, T. J., Macpherson, S., Qiu, S., Lebowitz, J., Wertz, G. W. & Luo, M. (2000). Study of the assembly of vesicular stomatitis virus N protein: role of the P protein. J Virol 74, 95159524.
Hamir, A. N., Moser, G., Fu, Z. F., Dietzschold, B. & Rupprecht, C. E. (1995). Immunohistochemical test for rabies: identification of a diagnostically superior monoclonal antibody. Vet Rec 136, 295296.[Medline]
Iseni, F., Barge, A., Baudin, F., Blondel, D. & Ruigrok, R. W. H. (1998). Characterization of rabies virus nucleocapsids and recombinant nucleocapsid-like structures. J Gen Virol 79, 29092919.[Abstract]
Kawai, A., Toriumi, H., Tochikura, T. S., Takahashi, T., Honda, Y. & Morimoto, K. (1999). Nucleocapsid formation and/or subsequent conformational change of rabies virus nucleoprotein (N) is a prerequisite step for acquiring the phosphatase-sensitive epitope of monoclonal antibody 5-2-26. Virology 263, 395407.[CrossRef][Medline]
Kouznetzoff, A., Buckle, M. & Tordo, N. (1998). Identification of a region of the rabies virus N protein involved in direct binding to the viral RNA. J Gen Virol 79, 10051013.[Abstract]
Mavrakis, M., Iseni, F., Mazza, C., Schoehn, G., Ebel, C., Gentzel, M., Franz, T. & Ruigrok, R. W. H. (2003). Isolation and characterization of the rabies virus N°-P complex produced in insect cells. Virology 305, 406414.[CrossRef][Medline]
Prehaud, C., Harris, R. D., Fulop, V., Koh, C. L., Wong, J., Flaman, A. & Bishop, D. H. L. (1990). Expression, characterization and purification of a phosphorylated rabies nucleoprotein synthesized in insect cells by baculovirus vectors. Virology 178, 486497.[Medline]
Rose, J. K. & Whitt, M. A. (2000). Rhabdoviridae: the viruses and their replication. In Fields Virology, 4th edition, pp. 12211240. Edited by D. M. Knipe, P. M. Howley, D. E. Griffin, R. A. Lamb, M. A. Martin, B. Roizman & S. E. Straus. Philadelphia, PA: LippincottRaven.
Schneider, L. G., Dietzschold, B., Dierks, R. E., Matthaeus, W., Enzmann, P. J. & Strohmaier, K. (1973). Rabies group-specific ribonucleoprotein antigen and a test system for grouping and typing of rhabdoviruses. J Virol 11, 748755.[Medline]
Schoehn, G., Iseni, F., Mavrakis, M., Blondel, D. & Ruigrok, R. W. (2001). Structure of recombinant rabies virus nucleoprotein-RNA complex and identification of the phosphoprotein binding site. J Virol 75, 490498.
Sokol, F. & Clark, H. F. (1973). Phosphoproteins, structural components of rhabdoviruses. Virology 52, 246263.[CrossRef][Medline]
Spehner, D., Drillien, R. & Howley, P. M. (1997). The assembly of the measles virus nucleoprotein into nucleocapsid-like particles is modulated by the phosphoprotein. Virology 232, 260268.[CrossRef][Medline]
Toriumi, H. & Kawai, A. (2004). Association of rabies virus nominal phosphoprotein (P) with viral nucleocapsid (NC) is enhanced by phosphorylation of the viral nucleoprotein (N). Microbiol Immunol 48, 399409.[Medline]
Wertz, G. W., Davies, N. L. & Patton, J. (1987). The role of proteins in vesicular stomatitis virus RNA replication. In The Rhabdoviruses, pp. 271296. Edited by R. R. Wagner. New York: Plenum.
Wu, X., Gong, X., Foley, H. D., Schnell, M. J. & Fu, Z. F. (2002). Both viral transcription and replication are reduced when the rabies virus nucleoprotein is not phosphorylated. J Virol 76, 41534161.
Wu, X., Lei, X. & Fu, Z. F. (2003). Rabies virus nucleoprotein is phosphorylated by cellular casein kinase II. Biochem Biophys Res Commun 304, 333338.[CrossRef][Medline]
Wunner, W. H. (1991). The chemical composition and molecular structure of rabies viruses. In Natural History of Rabies, 2nd edn, pp. 3167. Edited by G. M. Baer. Boca Raton, FL: CRC Press.
Yang, J., Hooper, D. C., Wunner, W. H., Koprowski, H., Dietzschold, B. & Fu, Z. F. (1998). The specificity of rabies virus RNA encapsidation by nucleoprotein. Virology 242, 107117.[CrossRef][Medline]
Yang, J., Koprowski, H., Dietzschold, B. & Fu, Z. F. (1999). Phosphorylation of rabies virus nucleoprotein regulates viral RNA transcription and replication by modulating leader RNA encapsidation. J Virol 73, 16611664.
Received 27 May 2004;
accepted 9 August 2004.
HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
INT J SYST EVOL MICROBIOL | MICROBIOLOGY | J GEN VIROL |
J MED MICROBIOL | ALL SGM JOURNALS |