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At least 19 recordsLinked to original sources
PubMed1985

ts1, a Paralytogenic mutant of Moloney murine leukemia virus TB, has an enhanced ability to replicate in the central nervous system and primary nerve cell culture.

A temperature-sensitive mutant of Moloney murine leukemia virus TB (MoMuLV-TB), ts1, which is defective in intracellular processing of envelope precursor protein (Pr80env), also possesses the ability to induce hind-limb paralysis in infected mice. To investigate whether ts1 has acquired neurotropism and to determine to what extent it can replicate in the central nervous system, we compared viral titers in the spleen, plasma, spinal cord, and brain throughout the course of infection of mice infected with ts1 and parental wild-type (wt) MoMuLV-TB. In both the ts1- and wt-inoculated mice, the concentrations of infectious virus recovered from the plasma and spleen increased rapidly and reached a plateau by 10 days postinfection (p.i.). In contrast, virus concentrations in the spinal cord and brain of ts1-inoculated mice increased gradually and reached a titer comparable to that in the spleen and exceeding that in the plasma only at 25 to 30 days p.i. At this time, the virus titer was approximately 200X greater in ts1-infected spinal cord tissue and approximately 20X greater in ts1-infected brain tissue than in the same wt-infected tissues. Paralysis became evident at 25 to 30 days p.i. in ts1-inoculated mice, whereas the wt-inoculated mice were normal. In addition, a substantial amount of Pr80env was detected in the spinal cords of ts1-inoculated mice compared with that found in the spinal cords of wt-inoculated mice. The infectious virus isolated from ts1-infected nerve tissue was found to possess the characteristic phenotype of the ts1 virus. Microscopic lesions of ts1-inoculated mice at 30 days p.i. consisted of vacuolar degeneration of motor neurons and spongy change of white matter in the brain stem and spinal cord. Similar but less severe lesions were observed in wt-inoculated mice. With primary cultures of central nervous system tissue we showed that ts1 can infect and replicate in both neuron and glial cells. In contrast, although wt MoMuLV-TB replicated in glial cell-rich culture, viral replication was barely detectable in neuron-rich culture.

Animals↗
PubMed1990

Site-directed mutagenesis of the codon for Ile-25 in gPr80env alters the neurovirulence of ts1, a mutant of Moloney murine leukemia virus TB.

ts1, a spontaneous temperature-sensitive mutant of Moloney murine leukemia virus TB, causes hind-limb paralysis in mice. A Val-25----Ile substitution in gPr80env is responsible for temperature sensitivity, inefficient processing of gPr80env, and neurovirulence. In this study, the Ile-25 in gPr80env was replaced with Thr, Ala, Leu, Gly, and Glu by site-directed mutagenesis of the codon for Ile-25 to generate a new set of mutant viruses, i.e., ts1-T, -A, -L, -G, and -E, respectively. The phenotypic characteristics of these mutant viruses differed from those of ts1. For each mutant, the degree of temperature sensitivity was correlated with the degree of inefficient processing of gPr80env, and the following rank order was observed for both parameters: ts1-E greater than ts1-G greater than ts1-L greater than ts1-A greater than ts1 greater than ts1-T. In FVB/N mice, mutant viruses of low and intermediate temperature sensitivity and inefficiency in processing of gPr80env were neurovirulent and consistently caused mutant-specific disease profiles: ts1-T caused severe whole-body tremor, ts1-A generally caused hind-limb paralysis, and ts1-L generally caused a delayed-onset paraparesis. By 150 days postinfection, FVB/N mice that were infected with ts1-G and -E, mutants of high temperature sensitivity and inefficiency in processing of gPr80env, had lymphoid leukemia instead of a neurological disease. These results suggest that the dynamics of gPr80env processing are important in determining the neurovirulent phenotype in vivo.

Animals↗
PubMed1991

Alteration from T- to B-cell tropism reduces thymic atrophy and cytocidal effects in thymocytes but not neurovirulence induced by ts1, a mutant of Moloney murine leukemia virus TB.

The ts1 mutant of Moloney murine leukemia virus TB causes degenerative neurologic and immunologic disease in mice, characterized by development of spongiform encephalomyelopathy resulting in hindlimb paralysis, marked thymic atrophy associated with immunodeficiency, and generalized body wasting. To investigate the pathogenesis of the thymic atrophy caused by ts1, we constructed a chimeric virus, ts1-Cas(NS), in which a major portion of the U3 region of the long terminal repeat of ts1, a T-lymphotropic and neurovirulent murine leukemia virus, was replaced by the corresponding U3 region of Cas-Br-E, a B-lymphotropic and neurovirulent murine leukemia virus. In FVB/N mice, ts1-Cas(NS) induced paralytic and wasting disease with incidence, severity, and latency similar to that induced by ts1, but it failed to cause thymic atrophy as severe as that observed in ts1-infected mice. Furthermore, thymocytes cultured from ts1-Cas(NS)-infected mice died at a much slower rate than those of ts1-infected mice. The U3 substitution in ts1-Cas(NS) specifically diminished the ability of the virus to replicate in the thymus, whereas viral replication in the spinal cord was not significantly affected; thus, neurovirulence was not changed. The correlation of reduced thymic atrophy with decreased thymic viral titers and the decreased ability of ts1-Cas(NS) to cause thymocyte death in mice suggest strongly that the marked thymic atrophy in ts1-infected mice is not an indirect effect occurring secondary to neurodegenerative and wasting disease but is a direct cytopathic effect of high-level viral replication in the thymus.

Animals↗
PubMed1992

ts1, a temperature-sensitive mutant of Moloney murine leukemia virus TB, can infect both CD4+ and CD8+ T cells but requires CD4+ T cells in order to cause paralysis and immunodeficiency.

When neonatal FVB/N mice were inoculated with ts1, a temperature-sensitive mutant of Moloney murine leukemia virus TB, they developed a progressive bilateral hindlimb paralysis and immunodeficiency leading to death 4 to 6 weeks after inoculation. T lymphocytes have been shown to be primarily responsible for this ts1-induced syndrome. Here we compare the role played by each subset of T lymphocytes, i.e., CD4+ and CD8+ T cells, in disease development. Mice were depleted of a specific subset for the first 10 days of their lives by using either anti-CD4 or anti-CD8 monoclonal antibodies in vivo. Disease development in these mice was then monitored. Depletion of CD4+ T cells significantly attenuated the ts1-induced syndrome: virus replication was decreased, disease latency was extended, and death was prevented in 60% of the mice. Similar treatment with anti-CD8 antibody had almost no effect on disease progression. However, when depletion was begun 2 weeks after neonatal ts1 inoculation, CD4+ T cell depletion did not affect disease development. ts1 infected CD4+ and CD8+ T lymphocytes equally well in vivo, as shown by flow cytometric analysis, but virus replication was restricted primarily to the CD4+ subset of T cells, as found by in vitro assay. Hence, CD4+ T lymphocytes play an important role in the development of ts1-induced paralysis and immunodeficiency. The mechanism of this CD4+ T-cell-mediated disease production by ts1 is not clear; however, increased replication of ts1 in the CD4+ T cells, especially in the early stages of the disease, seems to play a crucial role.

Animals↗
PubMed1991

Oligomerization and transport of the envelope protein of Moloney murine leukemia virus-TB and of ts1, a neurovirulent temperature-sensitive mutant of MoMuLV-TB.

Ts1, a temperature-sensitive mutant of Moloney murine leukemia virus-TB (MoMuLV-TB), causes a progressive hindlimb paralytic disease in susceptible strains of mice. Previously, it has been shown that a single amino acid substitution, Val-25----Ile in gPr80env, is responsible for the temperature sensitivity, inefficient transport, and processing of gPr80env at the restrictive temperature and the neurovirulence of ts1. Since the neurovirulence of ts1 is associated with inefficient transport and processing of gPr80env and since in other systems involving viral envelope proteins it has been shown that correct folding and oligomerization of envelope monomers are required for efficient transport, we have investigated the ability of gPr80env derived from either wild-type MoMuLV-TB or ts1 to associate into oligomeric complexes. In these experiments, we establish that at both the restrictive and the nonrestrictive temperatures gPr80env molecules derived from MoMuLV-TB associate to form oligomeric complexes and these oligomers are most likely trimers. gPr80env molecules derived from ts1 also oligomerize at both temperatures; however, at the restrictive temperature, most of the molecules within the trimeric complexes remain as gPr80env and are not processed to gp70 and Prp15E. These results indicate that lack of oligomerization of gPr80env is not responsible for the transport defect of ts1. Therefore, by interacting specifically with critical sites within target cells, oligomers of mutant gPr80env rather than "tangles" of monomeric viral envelope proteins may be involved in the neurodegenerative disorder produced by ts1.

Animals↗
PubMed1991

Construction and characterization of expression systems for the env gene of ts1, a mutant of Moloney murine leukemia virus-TB.

A temperature-sensitive mutant of the Moloney murine leukemia virus-TB, ts1, causes hindlimb paralysis and immunodeficiency in mice. At the restrictive temperature, the envelope precursor polyprotein, gPr80env, is inefficiently processed intracellularly, and this is associated with the neurovirulence of ts1. To test the hypothesis that expression of the envelope proteins of ts1 alone without infectious virus production can induce paralysis, it is necessary to use either transmissible retroviral expression vectors or microinjection of eukaryotic gene expression plasmid to introduce the env gene of ts1 into germlines of mice. In this study, we have constructed three retrovirus vectors and three gene expression plasmids, all of which contain the env gene of ts1. By comparing the different expression systems, we found that one construct, pts1-env(F) can express the envelope proteins at a level comparable to the level expressed in ts1-infected cells. Furthermore, the expressed envelope proteins of pts1-env(F)-transfected cells possess the phenotypes of the proteins expressed by the env gene of ts1.

Animals↗
PubMed1985

Molecular cloning of two paralytogenic, temperature-sensitive mutants, ts1 and ts7, and the parental wild-type Moloney murine leukemia virus.

ts1 and ts7, the paralytogenic, temperature-sensitive mutants of Moloney murine leukemia virus (MoMuLV), together with their wild-type parent, MoMuLV-TB, were molecularly cloned. ts1-19, ts7-22, and wt-25, the infectious viruses obtained on transfection to NIH/3T3 cells of the lambda Charon 21A recombinants of ts1, ts7, and wt, were found to have retained the characteristics of their non-molecularly cloned parents. In contrast to the wt virus, ts1-19 and ts7-22 are temperature-sensitive, inefficient in the intracellular processing of Pr80env at the restrictive temperature, and able to induce paralysis in CFW/D mice. Like the non-molecularly cloned ts7, the ts7-22 virion was also shown to be heat labile. The heat lability of the ts7 virion distinguishes it from ts1. Endonuclease restriction mapping with 11 endonucleases demonstrated that the base composition of MoMuLV-TB differs from that of the standard MoMuLV, but no difference was detected between the molecularly cloned ts1 and ts7 genomes. However, ts1 and ts7 differ from MoMuLV in the loss or acquisition of four different restriction sites, whereas they differ from MoMuLV-TB in the loss or acquisition of three different restriction sites.

Animals↗
PubMed1986

The neurovirulent determinants of ts1, a paralytogenic mutant of Moloney murine leukemia virus TB, are localized in at least two functionally distinct regions of the genome.

To better understand the molecular mechanism involved in retrovirus ts1-induced paralytic disease in mice, we constructed a panel of recombinant viruses between ts1 and the wild-type viruses Moloney murine leukemia virus (MoMuLV) and MoMuLV-TB, a strain of MoMuLV. These recombinant viruses were constructed in an attempt to identify the sequence(s) in the genome of ts1 which contains the critical mutation(s) responsible for the neurovirulence of ts1. Two functionally distinct sequences in the genome of ts1 were found to be responsible for its paralytogenic ability. One of these sequences, the 0.77-kilobase-pair XbaI-BamHI (nucleotides 5765 to 6537) fragment which encodes the 5' half of gp70 and 11 base pairs upstream of the env gene coding sequence, determines the inability of ts1 to process Pr80env. The other sequence, the 2.30-kilobase-pair BamHI-PstI (nucleotides 538 to 8264 and 1 to 567) fragment, which comprises nearly two-thirds of the env gene, the long terminal repeat, and the 5' noncoding sequence, determines the enhanced neurotropism of ts1. Replacement of any one of these two regions with the homologous region from either one of the two wild-type viruses resulted in recombinant viruses which either totally failed to induce paralysis or induced a greatly attenuated form of paresis in some of the infected mice.

Animals↗
PubMed1985

A 1.6-kilobase-pair fragment in the genome of the ts1 mutant of Moloney murine leukemia virus TB that is associated with temperature sensitivity, nonprocessing of Pr80env, and paralytogenesis.

ts1 and ts7, two temperature-sensitive mutants of Moloney murine leukemia virus strain TB induce hind-limb paralysis in 100% of CFW/D mice injected. These two paralytogenic mutants also share a defect in their inability to process the env precursor protein, Pr80env, at the restrictive temperature. To identify the mutation(s) in the genomes of the paralytogenic mutants which cause the inability to process Pr80env efficiently and confer the ability to cause hind-limb paralysis instead of lymphoma, we constructed chimeric genomes between ts1 and Moloney murine leukemia virus or the TB strain of the virus. We identified a 3.9-kilobase-pair HindIII-PstI sequence from nucleotides 4895 through 8264 and 1 through 567 of ts1, comprising the 3' end of the pol and all of the env genes, the long terminal repeat, and the 5' noncoding sequence, as being responsible for the temperature sensitivity, the inefficiency in processing Pr80env, and the induction of paralysis. We extended these findings by demonstrating that the 1.6-kilobase-pair pol-gp70 HindIII-BamHI DNA sequence from nucleotides 4895 through 6537 of ts1 within the 3.9-kilobase-pair HindIII-PstI fragment is necessary for ts1 to induce paralysis. In addition, we showed that this 1.6-kilobase-pair fragment also controls the processing of Pr80env and the temperature sensitivity of ts1.

Animals↗
PubMed1989

The role of the thymus in the pathogenesis of hind-limb paralysis induced by ts1, a mutant of Moloney murine leukemia virus-TB.

Newborn homozygous BALB/c nude (nu/nu) mice, their heterozygous (+/nu) littermates, and normal BALB/c (+/+) mice were infected with ts1, a paralytogenic mutant of Moloney murine leukemia virus-TB (MoMuLV-TB). Our results indicate that while infection of +/nu and +/+ mice with ts1 results in severe pathological changes in the central nervous system (CNS) and paralysis, infection of nu/nu mice results in only mild to moderate pathology within the CNS and no paralysis. On the other hand, 50% of nude mice reconstituted with T cells when infected with ts1 developed paralysis and showed more pronounced degeneration of nervous tissue than nude mice infected with ts1 alone. These observations strongly suggest that the thymus, the functional T lymphocytes, or both play an important role in the ts1-induced neurologic disorders in infected mice.

Animals↗
PubMed1990

A single amino acid change in E3 of ts1 mutant inhibits the intracellular transport of SFV envelope protein complex.

At 39 degrees the envelope protein complex (E1-p62) of Semliki Forest virus mutant ts1 is arrested in the rough endoplasmic reticulum (RER). When the infected cultures are shifted to 28 degrees, the complex is transported to the cell surface. During the transport p62 is cleaved into E2 under conditions in which no virus budding takes place. We have sequenced the cDNA, which encodes the envelope proteins of ts1. Comparison with the respective wild-type nucleotide sequence shows only one nucleotide change, G----A, causing a replacement of cysteine-58 (TGC) with tyrosine (TAC) in the E3 protein of ts1. A cDNA fragment from the ts1 genome encoding the mutation in E3 was used to replace the respective fragment of prototype SFV in an eukaryotic expression vector. Intracellular arrest of envelope proteins at 39 degrees was seen in transfected BHK21 cells. A shift of the transfected cells to 28 degrees resulted in the appearance of the envelope proteins at the cell surface. We conclude that the single point mutation is solely responsible for the temperature-sensitive transport defect of ts1 envelope glycoproteins.

Base Sequence↗
PubMed1991

High susceptibility of FVB/N mice to the paralytic disease induced by ts1, a mutant of Moloney murine leukemia virus TB.

The ts1 mutant of Moloney murine leukemia virus TB causes a degenerative neurologic and immunologic disease in susceptible strains of mice. This disease syndrome is characterized by development of spongiform encephalomyelopathy resulting in hindlimb paralysis, generalized bodywasting, and marked thymic atrophy associated with immune deficiency. The viral genetic determinants responsible for hindlimb paralysis in BALB/c and CFW/D mice have been localized to two point mutations in the env gene: one results in a Val-25----IIe substitution in the envelope precursor polyprotein gPr80env and the other, in an Arg-430----Lys substitution in the gp70. In this report we present studies showing that FVB/N mice were highly susceptible to ts1 and exhibited the shortest and most uniform latency period of all the murine strains tested. In addition, we have found that, unlike in CFW/D and BALB/c mice, only the Val-25----IIe substitution in the gPr80env is required to induce hindlimb paralysis in FVB/N mice. Our studies show that there was enhanced replication of ts1 in all tissues of FVB/N mice and that the virus titer in the spinal cord was more than 10-fold higher in FVB/N than in BALB/c mice by 30 days postinoculation, when the clinical signs of paralysis became evident in FVB/N mice. Apparently, other host factors that do not require the Arg-430----Lys substitution allowed high levels of viral replication within the central nervous system of FVB/N mice. These results, together with the finding that 100% of FVB/N mice that were inoculated with ts1 at 5 days of age developed hindlimb paralysis at 30-60 days postinoculation, whereas only 33% of 5-day-old BALB/c mice developed hindlimb paralysis with a much longer latency period, suggest that subtle virus-host interactions determine the incidence, the latency period, and the severity of the disease caused by ts1.

Aging↗
PubMed1991

T, not B, lymphocytes are required for immunodeficiency and paralysis induced by ts1, a mutant of Moloney murine leukemia virus-TB.

BALB/c mice when injected as newborn with ts1, a temperature-sensitive mutant of Moloney murine leukemia virus-TB, developed a fatal hindlimb paralysis and immunodeficiency. This disease induction was prevented, to a great extent, by transient depletion of the peripheral T lymphocytes during the early course of infection by using anti-Thy 1.2 antibody. FVB/N mice, which are highly susceptible to ts1, but express Thy 1.1 instead of Thy 1.2 on their T lymphocytes, did not show any difference in the disease profile when treated similarly with anti-Thy 1.2 antibody. Transient depletion of the peripheral B lymphocytes in BALB/c mice in the early course of ts1 infection had no effect on the disease induction. In the T cell depleted BALB/c mice, virus replication was reduced, survival of the mice was increased and viral specific antibodies were produced, whereas, in the B cell depleted mice the disease process went on in a fashion similar to untreated mice infected with ts1. Thus, this study demonstrates that the disease syndrome induced by ts1 in BALB/c mice is dependent upon the presence of T lymphocytes during the early course of infection, and that presence of B lymphocytes have little or no effect on the disease outcome.

Animals↗
PubMed1989

ts1, a mutant of Moloney murine leukemia virus-TB, causes both immunodeficiency and neurologic disorders in BALB/c mice.

BALB/c mice infected with ts1, a mutant of Moloney murine leukemia virus-TB, develop generalized body wasting, profound neurologic disorders, severe thymic atrophy and lymphopenia due to destruction of T lymphocytes and drastic immunodeficiency. ts1 was found not only able to infect T lymphocytes but also to impair their function. In addition, ts1 also infects and induces syncyntia formation in macrophages. The genetic determinant(s) responsible for ts1's ability to induce immunodeficiency has been localized to the env gene.

Animals↗
PubMed1988

Identification of point mutations in the envelope gene of Moloney murine leukemia virus TB temperature-sensitive paralytogenic mutant ts1: molecular determinants for neurovirulence.

ts1, a temperature-sensitive mutant of Moloney murine leukemia virus TB, induces hind-limb paralysis in mice. The DNA of both the ts1 and Moloney murine leukemia virus TB env genes has been sequenced, and the encoded amino acid sequences have been deduced from the DNA sequences. Four amino acids in the ts1 envelope protein have been identified which may be responsible for the ts1 phenotype, which includes temperature sensitivity, nonprocessing of Pr80env, and neurovirulence.

Amino Acid Sequence↗
PubMed1987

Role of cell cytoskeleton in Mo-MuLV env transport and processing: implications in ts1 neuropathology.

Treatment of Mo-MuLV-infected cells with cytochalasin B (CB), a microfilament disrupting drug, caused a reduction in virus yield as judged by infectivity assay and reverse transcriptase activity. Pulse-chase experiments with [3H]leucine showed that the env precursor, gPr80env, was inefficiently processed in cells treated with CB. In the presence of monensin, an inhibitor of glycoprotein transport, gPr80env accumulated intracellularly and no gp70 was observed on the cell surface, indicating a complete block in the processing of gPr80env. Pulse-chase studies also showed that gPr80env was not processed in the presence of monensin. SDS-PAGE analysis of TX-100-extracted cell cytoskeletons (TX-insoluble fraction) iodinated and immunoprecipitated with goat anti-gp70 antiserum showed that CB or monensin treatment caused a marked increase of gPr80env in the cytoskeleton-rich fraction. However, the amount of gPr80env associated with the TX-soluble fraction in both CB or monensin-treated and untreated cells labeled with [3H]leucine was about the same. The gPr80env in the TX-100-soluble fraction of the cell was the endoglycosidase H (Endo-H) sensitive mannose-rich form, whereas the cytoskeleton-associated gPr80env was the partially Endo-H-resistant complex carbohydrate form. In the presence of CB or monensin, the complex carbohydrate form of gPr80env accumulated in the cytoskeleton-rich cell fraction. Examination of Mo-MuLV ts1 mutant, which is defective in the processing of env precursor polyprotein, also revealed an accumulation of the complex carbohydrate form of gPr80env in the cytoskeleton-rich fraction and an absence of gp70 on the surface of the cell at the restrictive temperature (39 degrees C). These studies suggest that the cytoskeleton plays a role in the transport and processing of MuLV gPr80env and that oligosaccharide conversion is an important factor in this process. Further, the accumulation of gPr80env on the cytoskeleton of ts1 infected cells at restrictive temperature may play a role in the neurological disorder caused by Mo-MuLV ts1 mutant.

Animals↗
PubMed1990

A Val-25-to-Ile substitution in the envelope precursor polyprotein, gPr80env, is responsible for the temperature sensitivity, inefficient processing of gPr80env, and neurovirulence of ts1, a mutant of Moloney murine leukemia virus TB.

ts1 is a neurovirulent spontaneous temperature-sensitive mutant of Moloney murine leukemia virus TB which causes hindlimb paralysis in mice. Previously, it had been shown that the temperature-sensitive defect resided in the env gene. At the restrictive temperature, the envelope precursor polyprotein, gPr80env, is inefficiently processed intracellularly into two cleavage products, gp70 and Prp15E. This inefficient processing of gPr80env is correlated with neurovirulence. In this study, it was shown that a single amino acid substitution, Val-25----Ile in gPr80env, is responsible for the temperature sensitivity, inefficient processing of gPr80env at the restrictive temperature, and neurovirulence of ts1. At the restrictive temperature, a steady-state level of nonprocessed, endoglycosidase H-sensitive gPr80env remained in the endoplasmic reticulum of cells infected by ts1, but no endoglycosidase H-resistant gPr80env and only trace amounts of gp70 were detected in the infected cells. Since the host cell-encoded processing protease resides in the cis cisternae of the Golgi apparatus, inefficient processing of gPr80env at the restrictive temperature is most likely due to inefficient transport of gPr80env from the endoplasmic reticulum to the cis cisternae of the Golgi apparatus rather than due to misfolded gPr80env being a poor substrate for the processing protease at the restrictive temperature.

Animals↗
PubMed1977

Ultrastructural studies of H-1 parvovirus replication. IV. Crystal development and structure with the temperature-sensitive mutant ts1.

Electron microscopy was used to study the development and structure of viral crystals of ts1, a temperature-sensitive mutant of H-1 parvovirus. At early times postinfection, at the restrictive temperature, empty H-1 capsids aggregated to form conspicuous noncrystalline conglomerates in human NB cell nuclei; these particles did not associate with euchromatin as in wild-type H-1 infections. Later on, the capsid aggregated appeared to form polycrystals exhibiting rod-like, hexagonal, and cubic patterns that were interconvertible using a goniometer specimen stage. The unit cell of this crystal was cubic, consisted of 16 empty particles, and measured 50 nm on each side. Full particles made at the permissive temperature were never observed under restrictive conditions. Experiments in which cultures were shifted form the permissive to the restrictive temperature showed that full virions were not incorporated into crystals. The crystals dissociated into individual particles when changes were made from restrictive to permissive conditions. Correlations between the formation of crystals at the restrictive temperature, their dissociation into capsid components after shifting from the restrictive to the permissive state, and the extent of host cell damage were also observed. Possible roles of cellular functions in regulating ts1 H-1 polycrystal assembly and dissociation are discussed.

Capsid↗