Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Virus Assembly”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1977

Phosphorylation and nucleic acid binding properties of m1 Moloney murine sarcoma virus-specific pP60gag.

The pP60gag polyprotein of the feline leukemia virus pseudotype of m1 Moloney murine sarcoma virus [m1MSV(FeLV)] was previously shown to be MSV specific and to contain murine p30 and smaller structural polypeptides. This protein was detected in m1MSV-transformed cells, and in pulse-chase studies it was found to be stable. In this study virion P60 was shown to contain murine pp12, to be phosphorylated, and to bind to nucleic acids. 32P-labeled m1MSV[FeLV) was fractionated by guanidine agarose chromatography and analyzed by gel electrophoresis. Both P60 and pp12 were found to be the major phosphoproteins, phosphorylated in both serine and threonine residues. Virion P60 bound preferentially to single-stranded DNA and RNA in a competition filter binding assay, using 125I-labeled single-stranded calf thymus DNA and various unlabeled nucleic acids. Similar phosphorylation and DNA binding properties were demonstrated for cellular P60. Thus, immunoprecipitation of cellular extracts showed that P60 was phosphorylated in both producer and nonproducer transformed cells, indicating that phosphorylation occurs independently of virus assembly. Moreover, P60 from cytoplasmic extracts was retained on single-stranded DNA-Sepharose columns, demonstrating that cellular P60 binds to DNA.

DNA↗
PubMed1978

Expression of "early" and "late" viral functions in a somatic cell hybrid between a mouse cell and a spontaneous yielder SV 40-transformed Chinese hamster cell.

A somatic cell hybrid (Cl. 6d) was originated from the fusion of mouse 3T3-4E) and spontaneous yielder SV 40-transformed Chinese hamster (CHK/SVLP AG) cells. During the early stages of its history, the C1. 6d hybrid underwent a rapid chromosome loss, preferentially loosing hamster chromosomes. This was not a constant tendency of the hybrid cells. As the parental CHK)SVLP AG cells, the hybrid cells were always found 100 per cent SV40 T-antigen positive. While CHK/SVLP AG cells infectious SV 40 DNA, V-antigen and virus were regularly detected, in the hybrid cells only infectious DNA was occasionally detected. This was not due either to the loww of an essential Chinese hamster gene(s) or to the presence of an inhibiting mouse cell component(s); it was apparently the consequence of inability of the cells to properly activate the resident SV 40 genome(s). After superinfection with SV 40 DNA, the hybrid cells-though capable of synthesizing SV 40 V-antigen--were unable to ensure virus assembly. Experimental evidence was obtained suggesting that SV 40 maturation is dependent of a cellular function(s).

Animals↗
PubMed1978

Cycloleucine blocks 5'-terminal and internal methylations of avian sarcoma virus genome RNA.

Cycloleucine, a competitive inhibitor of ATP: L-methionine S-adenosyltransferase in vitro, has been used to reduce intracellular concentrations of S-adenosylmethionine and by this means to inhibit virion RNA methylation in chicken embryo cells that are infected with B77 avian sarcoma virus. Under conditions of cycloleucine treatment, where virus production as measured by incorporation of radioactive precursors or by number of infectious particles is not significantly affected, the internal m6A methylations of the avian sarcoma virus genome RNA are inhibited greater than 90%. The predominant 5'-terminal structure in viral RNA produced by treated cells in m7G(5')pppG (cap zero) rather than m7G-(5')pppGm (cap 1). It appears from these results that internal m6A and penultimate ribose methylations are not required for avian sarcoma RNA synthesis and function. Furthermore, these methylations are apparently not required for transport of genome RNA to virus assembly sites. The insensitivity of the 5'-terminal m7G methylation to inhibition by cycloleucine suggests that the affinity of S-adenosylmethionine for 7-methylguanosine methyltransferase is significantly greater than for the 2'-0-methyltransferases or the N6-methyltransferases.

Amino Acids↗
PubMed1979

The errors in assembly of MuLV in interferon treated cells.

Interferon treatment of JLSV-6 cells chronically infected with Rauscher MuLV leads to the formation of noninfectious particles (interferon virions) containing the structural proteins of env and gag genes as well as additional viral polypeptides. In the control virions the major glycoprotein detected is gp71, interferon virions contain in addition to gp71 and 85k dalton (gp85) glucosamine-containing, fucose-deficient glycoprotein which is recognized by antiserum to MuLV but not by the gp71 antiserum. The surface iodination of the intact virions indicates that both gp71 and gp85 are the major components of the external virions envelope. However, unlike the control virions in which gp71 associates with p15E (gp90), the gp71-p15E complex was not detected in interferon virions. The analysis of the iodinated proteins of the disrupted interferon virions revealed the presence of 85k and 65k dalton polypeptides preciptable with antiserum against MuLV, which are not present in the control virions. The difference in the polypeptide pattern of virions produced in the presence of interferon does not seem to be a consequence of the slowdown in the synthesis of viral proteins or their processing in the interferon-treated cells. Both the structural proteins of env and gag genes seem to be synthesized and processed at a comparable rate in the interferon-treated and -untreated cells. These results indicate an alteration of virus assembly in the presence of interferon.

Animals↗
PubMed1978

The carboxyl-terminal sequence of the heavy chain of a Hong Kong influenza haemagglutinin.

The reduced carboxymethylated heavy chain (HA1) of a Hong Kong influenza haemagglutinin (H3) was digested with cyanogen bromide to give five peptides. The sequences of three of these peptides, together with the sequences of two methionine overlap peptides were combined to give the C-terminal 68-residue sequence of the heavy chain. Threonine is the C-terminal residue of the heavy chain, an unexpected result in view of the generation of the heavy and light chains by the proteolytic cleavage of a pro-haemagglutinin during virus assembly. Three half-cystine residues occur close together at positions 24, 48 and 52 residues in from the C-terminus. A carbohydrate group is attached to an asparagine residue 44 residues from the C-terminus; it contains 5 residues mannose and 2 residues glucosamine.

Amino Acid Sequence↗
PubMed1979

Subfractionation of CsCl-purified H-1 parvovirus on metrizamide gradients.

The different density classes of H-l parvovirus, collected within 30 hr of infection of par-asynchronous cultures, following the standard CsCl purification step, have been shown to be heterogeneous. Rebanding of the denser form (HF, p = 1.46 g/cm3) and the less dense form (LF, p = 1.42 g/cm3) of infectious virus in the nonionic density generating solute, metrizamide, showed that both HF and LF virus bands were heterogeneous in density. The infectivity banded with isotopically labeled virus protein and DNA at 1.32 g/cm3 for both HF and LF virus. Amounts of protein and DNA which varied from preparation to preparation, but which were greater from the HF virus band, were distributed throughout the rest of the gradient, but predominated in a peak at a density of 1.2 g/cm3. The protein in this peak was without hemagglutinating activity but had the molecular weights and proportions of the H-l virion proteins (VPl, VP2', and VPZ). The DNA was of the same size as H-l DNA monomers and its proportion to the protein was similar to that of the infectious peak. The DNA was susceptible to micrococcal nuclease digestion. The nature of this noninfectious viral material thus seemed to be incompletely assembled virus. Radiolabeled H-l virus collected after 72 hr of infection formed a discrete single peak in both CsCl (p = 1.42 g/cm3), and metrizamide gradients (p = 1.32 g/cm3). There was no significant amount of the 1.20 g/cm3 viral protein-DNA complex in these mature preparations.

Centrifugation, Density Gradient↗
PubMed1979

Location and encapsidation of the coat protein cistron of tobacco mosaic virus. A bidirectional elongation of the nucleoprotein rod.

The coat protein cistron of tobacco mosaic virus has been located on the viral RNA starting between 975 and 1050 nucleotides from the 3'-hydroxyl end. This locates its 5' end close to the origin for virus assembly, where the first protein disk interacts with RNA. It also means that the coat protein mRNA must have a short 5'-untranslated tail and a long (over 500 nucleotides) 3' one. The recovery of characteristic oligonucleotides in nuclease-protected rods during the growth from RNA and a protein disk preparation shows that elongation of the nucleated rods proceeds independently in both directions though, on average, much more rapidly along the longer 5' tail than the shorter 3' tail. Protected RNA of length equal to that in the complete virion is first seen within 6 min, showing that the most rapidly elongated particles are substantially complete by this time.

Base Sequence↗
PubMed1978

Folate polyglutamates in T4D bacteriophage and T4D-infected Escherichia coli.

The folate compound which is a structural component of the Escherichia coli T-even bacteriophage baseplates, has been identified as the hexaglutamyl form of folic acid using a new chromatographic procedure (Baugh, C.M., Braverman, E. and Nair, M.G. (1974) Biochemistry 13, 4952-4957). It has also been found that the host cell contains a variety of polyglutamyl forms of folic acid. The major form is the triglutamate (about 50%) but small amounts of higher molecular weight folates including the octaglutamate (1.8%) have been identified. Upon infection with wild-type T4D bacteriophage there is a shift in the distribution of the folate compounds so that the folyl polyglutamyl compounds having the higher molecular weights are increased. Infection of E. coli with baseplate mutants of T4D containing an amber mutation in gene 28 resulted in the formation of significant amounts (over 7%) of folate compound(s) of molecular weight much higher than those observed either in uninfected cells or cells infected with wild-type T4D. It is suggested that the T4D gene 28 product functions to cleave glutamate residues from high molecular weight folyl polyglutamates to increase the availability of the folyl hexaglutamate for virus assembly.

Coliphages↗
PubMed1976

Adenovirus protein maturation at 42 degrees C.

Incubation of adenovirus type 2 infected cells at 42 degrees C resulted in an inhibition of assembly of virus particles although all the major viral structural polypeptides and virus-induced cellular polypeptides so far identified were detected by electrophoretic analysis. Selective high salt-acid-urea extraction of low mol. wt. polypeptides revealed the absence of protein VII at 42 degrees C whereas precursor polypeptide P-VII and core protein V were found. Pulse-chase and temperature shift experiments indicated that cleavage of P-VII into VII was a reversible thermosensitive process, requiring de novo protein synthesis after shift-down to 37 degrees C. Virus particles assembled at 37 degrees C after transfer from 42 to 37 degrees C contained both viral DNA and polypeptides pre-labelled during the eclipse phase at 42 degrees C, including core protein VII.

Adenoviridae↗
PubMed1979

Characterization of two temperature-sensitive mutants of adenovirus type 5.

The properties of two temperature-sensitive mutants ts 18 and ts 19 of adenovirus type 5 were studied. It was demonstrated that they had a defect such that they failed to assemble virus and showed defective processing of infected cell polypeptides at the restrictive temperature. Analysis, after protease digestion, of the virions produced at the permissive temperature by SDS PAGE, and of the substrate availability of the mutants to the virus protein kinase suggested that polypeptide VI was defective in these mutants.

Adenoviruses, Human↗
PubMed1976

Assembly of flexuous plant viruses and their proteins.

Recent experiments on the disassembly and assembly of some flexuous plant viruses and their proteins are described. The properties of reconstituted potato virus X and those of assembled potato virus Y protein are considered as well as the suitability of other flexuous viruses for reconstitution studies.

Plant Viruses↗
PubMed2025

Discovery of bimodal hepatitis B virus ribonuclease H and capsid assembly inhibitors.

Hepatitis B virus (HBV) ribonuclease H (RNaseH) inhibitors are a potent class of antivirals that prevent degradation of the viral pregenomic RNA during reverse transcription and block formation of mature HBV DNAs. Development of HBV RNaseH inhibitors is entering advanced preclinical analyses. To ensure the mechanism of action was fully understood, we defined the effects of RNaseH inhibitors on other steps of HBV replication. Some N-hydroxypyridinedione (HPD) HBV RNaseH inhibitors significantly reduced accumulation of capsids in HBV-replicating cells. A representative HPD 1466, with a 50% effective concentration against HBV replication of 0.25 µM, decreased capsid and core protein accumulation by 50-90% in HepDES19 and HepG2.2.15 cells. Surprisingly, 1466 did not affect pregenomic RNA encapsidation, demonstrating a specific effect on empty capsids. HBV genomic replication was not necessary for 1466's inhibitory effect as it decreased capsid accumulation in cells transfected with replication-deficient mutants blocking pgRNA encapsidation (Δ-bulge), DNA synthesis (YMHA), and RNaseH (D702A) activities. 1466 also decreased capsid and core protein accumulation in cells transfected with a core protein expression plasmid, indicating that other HBV products are unneeded. 1466 reduced initial capsid assembly rates in biochemical assembly reactions employing purified core protein (Cp149), demonstrating a specific effect on HBV core protein. We conclude that the bimodal HPD HBV RNaseH inhibitor 1466 is the prototypic member of a new class of capsid assembly modulators (CAM) that inhibits capsid assembly rather than accelerating it, as all other CAM classes do. We propose that this class be called CAM-I, for CAM-inhibitor. These results lay the foundation for identifying bimodal HBV antivirals targeting the RNaseH and capsid assembly.

Hepatitis B virus↗
PubMed1977

Electron microscopic characterization of the defectiveness of a temperature-sensitive mutant of Moloney murine leukemia virus restricted in assembly.

The effect of temperature shiftdown on the assembly of ts3 virions was investigated by both scanning (SEM) and transmission (TEM) electron microscopy. Ts3 is a spontaneous temperature-sensitive mutant of Moloney murine leukemia virus (Mo-MuLV) which previous studies indicated to be defective in assembly or release of the virions. In the present study, both SEM and TEM revealed the following: (i) there were more cell-associated virions in ts3-infected cells grown at the nonpermissive temperature (39 degrees C) than either in cells grown at the permissive temperature (34 degrees C) or in wild-type MuLV-infected cells grown at 39 degrees C; (ii) there were more normal single particles than multiploids (virions with two or more pieces of genomic RNA) in ts3-infected cells grown at the nonpermissive temperature; (iii) there were more multiploids in ts3-infected cells grown at the nonpermissive temperature than either in cells grown at the permissive temperature or in wild-type MuLV-infected cells grown at the nonpermissive temperature; (iv) upon temperature shift from 39 to 34 degrees C, about 90% of the cell-associated virions dissociated from the cell surface. TEM studies also indicated that upon temperature shiftdown, virion assembly rapidly occurred. The above observations suggest that faulty assembly, which results in the production of multiploids, may not be the reason why ts3 virions accumulate on the cell surface at the nonpermissive temperature. The relatively higher proportion of multiploids found in ts3-infected cells grown at 39 degrees C compared with those grown at 34 degrees C may be due to the higher density of budding virions at the cell surface at the nonpermissive temperature, which increases the possibility of two or more particles assembling close to one another. The accumulation of ts3 virions in all stages of assembly at the nonpermissive temperature, together with the fact that rapid assembly and release of ts3 virions occurred on temperature shiftdown, indicates that virion assembly is restricted after it has been initiated. The probable role of altered glycoprotein(s) in restricting virion assembly is discussed.

Cell Line↗
PubMed1976

Synthesis of murine leukemia virus proteins associated with virions assembled in actinomycin D-treated cells: evidence for persistence of viral messenger RNA.

Murine leukemia virus particles assembled in actinomycin D-treated cells were detected by determination of reverse transcriptase [RNA-dependent DNA polymerase (nucleotidyltransferase)] activity and by radioimmunoassay of the major virion protein, p30. The levels of enzyme activity and p30 protein were both 30-40% relative to the control over an 8 hr period, whereas after 3 or 4 hr infectivity was reduced by 95%. Thus, virions produced in the absence of RNA synthesis represent a fairly homogeneous population of defective particles. Although RNA synthesis is not necessary for virus assembly, protein synthesis is required. Treatment of cells with 10 mug/ml of cycloheximide reduced virus production by 80-85% within 2 hr, and by greater than 95% at later times. As might be expected from this finding, viral protein synthesis accompanies virus assembly in actinomycin D-treated cells. Newly synthesized proteins associated with the defective particles were identical with those found in standard virions and were present in the correct proportions. The results demonstrate that viral mRNA persists in cells in which RNA synthesis is blocked and continues to direct viral protein synthesis with a functional half-life of approximately 6-8 hr. Since viral mRNA is not packaged in virions even when viral RNA synthesis is shut off [Levin et al. (1974) J. Virol. 14, 152-161], we propose that murine leukemia virus-infected cells contain two nonequilibrating pools of intracellular viral RNA molecules, one associated with polyribosomes and one which is encapsidated into extracellular particles.

AKR murine leukemia virus↗
PubMed2022

Atomic model of vesicular stomatitis virus and mechanism of assembly.

Like other negative-strand RNA viruses (NSVs) such as influenza and rabies, vesicular stomatitis virus (VSV) has a three-layered organization: a layer of matrix protein (M) resides between the glycoprotein (G)-studded membrane envelope and the nucleocapsid, which is composed of the nucleocapsid protein (N) and the encapsidated genomic RNA. Lack of in situ atomic structures of these viral components has limited mechanistic understanding of assembling the bullet-shaped virion. Here, by cryoEM and sub-particle reconstruction, we have determined the in situ structures of M and N inside VSV at 3.47 Å resolution. In the virion, N and M sites have a stoichiometry of 1:2. The in situ structures of both N and M differ from their crystal structures in their N-terminal segments and oligomerization loops. N-RNA, N-N, and N-M-M interactions govern the formation of the capsid. A double layer of M contributes to packaging of the helical nucleocapsid: the inner M (IM) joins neighboring turns of the N helix, while the outer M (OM) contacts G and the membrane envelope. The pseudo-crystalline organization of G is further mapped by cryoET. The mechanism of VSV assembly is delineated by the network interactions of these viral components.

Animals↗
PubMed1975

Evidence for the existence of protomers in the assembly of encephalomyocarditis virus.

Two capsid precursor subunits, which sediment on glycerol gradients at 13S and 14S, respectively, have been identified in cytoplasmic extracts of encephalomyocarditis virus-infected HeLa cells. The 13S subunit, which was detected after a 10-min pulse label with -3H-labeled amino acids, contained only capsid precursor chain A (mol wt 100,000). When the 10-min pulse label in such cells was chased for 20 min, the A-containing 13S subunit in the cytoplasmic extracts was replaced by a 14S subunit containing equimolar proportions of three chains: epsilon, gamma, and alpha. This (epsilon, gamma, alpha)-containing 14S subunit could be dissociated into 6S subunits with the same polypeptide composition. The sedimentation properties and the polypeptide stoichiometry of these three precursor subunits, when compared with those of the 13S, (beta, gamma, alpha)(5), and 5S, (beta, gamma, alpha), subunits derived by acid dissociation of purified virions, suggest the following structural assignments: 13S, (A)(5); 14S, (epsilon, gamma, alpha)(5), 6S, (epsilon, gamma, alpha). The molecular weights of the individually isolated capsid chains were determined by gel filtration in 6 M guanidine hydrochloride to be: epsilon, 36,000; alpha, 32,000; beta, 29,500; gamma, 26,500; and delta, 7,800. With the exception of the delta-chain, these values are in reasonable agreement with the values previously determined by electrophoresis on sodium dodecyl sulfatepolyacrylamide gels. These data support the hypothesis that picornavirus capsids are assembled from identical protomers according to the following scheme: (A) leads to (A)(5) leads to (epsilon, gamma, alpha)(5) leads to (delta, beta, gamma, alpha)60-n(epsilon, gamma, alpha)n where n is the number of immature protomers per virion.

Amino Acids↗