Mechanism by which fiber antigen inhibits multiplication of type 5 adenovirus

Effect of Genetic Modifications on Physical and Functional Titers of Adenoviral Cancer Gene Therapy Constructs

After the discovery and characterization of the adenovirus in the 1950s, this prevalent cause of the common cold and other usually mild diseases has been modified and utilized in biomedicine in several ways. To date, adenoviruses are the most frequently used vectors and therapeutic (e.g., oncolytic) agents with a number of beneficial features. They infect both dividing and nondividing cells, enable high-level, transient protein expression, and are easy to amplify to high concentrations. As an important and versatile research tool, it is of essence to understand the limits and advantages that genetic modification of adenovirus vectors may entail. Therefore, a retrospective analysis was performed of adenoviral gene therapy constructs produced in the same laboratory with similar methods. The aim was to assess the impact of various modifications on the physical and functional titer of the virus. It was found that genome size (designed within "the 105% golden rule") did not significantly affect the physical titer of the adenovirus preparations, regardless of the type of transgene (e.g., immunostimulatory vs. other), number of engineered changes, and size of the mutated virus genome. One statistically significant exception was noted, however. Chimeric adenoviruses (5/3) had a slightly lower physical titer compared to Ad5-based viruses, although a trend for the opposite was true for functional titers. Thus, 5/3 chimeric viruses may in fact be appealing from a safety versus efficacy viewpoint. Armed viruses had lower functional and physical titers than unarmed viruses, while five genomic modifications started to decrease functional titer. Importantly, even highly modified armed viruses generally had good titers compatible with clinical testing. In summary, this paper shows the plasticity of adenovirus for various vector, oncolytic, and armed oncolytic uses. These results inform future generations of adenovirus-based drugs for human use. This information is directly transferable to academic laboratories and the biomedical industry involved in vector design and production optimization.

DT. Targeting lung cancer using an infectivity enhanced CXCR4-CRAd

Conventional treatments are not adequate for the majority of lung cancer patients. Conditionally replicating adenoviruses (CRAds) represent a promising new modality for the treatment of neoplastic diseases, including non-small cell lung cancer. Specifically, following cellular infection, the virus replicates selectively in the infected tumor cells and kills the cells by cytolysis. Next, the progeny virions infect a new population of surrounding target cells, replicate again and eradicate the infected tumor cells while leaving normal cells unaffected. However, to date, there have been two main limitations to successful clinical application of these CRAd agents; i.e. poor infectivity and poor tumor specificity. Here we report the construction of a CRAd agent, CRAd-CXCR4.RGD, in which the adenovirus E1 gene is driven by a tumor-specific CXCR4 promoter and the viral infectivity is enhanced by a capsid modification, RGD4C. This agent CRAd-CXCR4.RGD, as expected, improved both of the viral infectivity and tumor specificity as evaluated in an established lung tumor cell line and in primary tumor tissue from multiple patients. As an added benefit, the activity of the CXCR4 promoter was low in human liver as compared to three other promoters regularly used for targeting tumors. In addition, this agent has the potential of targeting multiple other tumor cell types. From these data, the CRAd-CXCR4.RGD appears to be a promising novel CRAd agent for lung cancer targeting with low host toxicity.

Structural basis for variation in adenovirus affinity for the cellular coxsackievirus and adenovirus receptor

The majority of adenovirus serotypes can bind to the coxsackievirus and adenovirus receptor (CAR) on human cells despite only limited conservation of the amino acid residues that comprise the receptor-binding sites of these viruses. Using a fluorescence anisotropy-based assay, we determined that the recombinant knob domain of the fiber protein from adenovirus serotype (Ad) 2 binds the soluble, N-terminal domain (domain 1 (D1)) of CAR with 8-fold greater affinity than does the recombinant knob domain from Ad12. Homology modeling predicted that the increased affinity of Ad2 knob for CAR D1 could result from additional contacts within the binding interface contributed by two residues, Ser408 and Tyr477, which are not conserved in the Ad12 knob. Consistent with this structural model, substitution of serine and tyrosine for the corresponding residues in the Ad12 knob (P417S and S489Y) increased the binding affinity by 4- and 8-fold, respectively, whereas the double mutation increased binding affinity 10-fold. X-ray structure analysis of Ad12 knob mutants P417S and S489Y indicated that both substituted residues potentially could form additional hydrogen bonds across the knob-CAR interface. Structural changes resulting from these mutations were highly localized, implying that the high tolerance for surface variation conferred by the stable knob scaffold can minimize the impact of antigenic drift on binding specificity and affinity during evolution of virus serotypes. Our results suggest that the interaction of knob domains from different adenovirus serotypes with CAR D1 can be accurately modeled using the Ad12 knob-CAR D1 crystal structure as a template.

Mutations in the DG loop of adenovirus type 5 fiber knob protein abolish high-affinity binding to its cellular receptor CAR

The amino acid residues in adenovirus type 5 (Ad5) fiber that interact with its cellular receptor, the coxsackie B virus and Ad receptor (CAR), have not been defined. To investigate this, multiple mutations were constructed in the region between residues 479 and 497 in Ad5 fiber (beta-strands E and F and the adjacent region of the DG loop). The effects of these mutations on binding to CAR were determined by use of cell-binding competition experiments, surface plasmon resonance, and direct binding studies. The mutation effects on the overall folding and secondary structure of the protein were assessed by circular dichroism (CD) spectroscopy. Deletions of two consecutive amino acids between residues 485 and 493 abolished high-affinity binding to CAR; the CD spectra indicated that although there was no disruption of the overall folding and secondary structure of the protein, local conformational changes did occur. Moreover, single site mutations in this region of residues with exposed, surface-accessible side chains, such as Thr492, Asn493, and Val495, had no effect on receptor binding, which demonstrates that these residues are not in contact with CAR themselves. This implies the involvement of residues in neighboring loop regions. Replacement of the segment containing the two very short beta-strands E and F and the turn between them (residues 479 to 486) with the corresponding sequence from Ad3 (betaEFAd3-->5 mutation) resulted in the loss of receptor binding. The identical CD spectra for betaEFAd3-->5 and wild-type proteins suggest that these substitutions caused no conformational rearrangement and that the loss of binding may thus be due to the substitution of one or more critical contact residues. These findings have implications for our understanding of the interaction of Ad5 fiber with CAR and for the construction of targeted recombinant Ad5 vectors for gene therapy purposes.

A single locus on human chromosome 21 directs the expression of a receptor for adenovirus type 2 in mouse A9 cells

The receptors on human cells which mediate adsorption of adenoviruses have not been identified. We found that murine A9 cells and Chinese hamster ovary (CHO) cells failed to bind significant levels of radiolabeled adenovirus type 2 (Ad2) virions but that derivatives of these cells carrying human chromosome 21 exhibited high levels of virus binding that was specific for the viral fiber protein. G418-resistant A9 cell transformants expressing Ad2 receptors were detected at a frequency of about 10(-4) following cotransfection with high-molecular-weight DNAs from mouse cells containing human chromosome 21 and plasmid DNA containing a neomycin resistance gene. The Ad2 receptors on the transformed A9 cells were similar to those on human cells with respect to their concentration on the cell membrane, their affinity for the viral fiber protein, and their ability to direct virus into cells along a pathway leading to delivery of the viral DNA genome into the cell nucleus. Furthermore, identical human DNA fragments were present in three independent mouse cell transformants expressing Ad2 receptors, supporting the conclusion that these human DNA fragments correspond to a gene or locus on chromosome 21 that directs the expression of Ad2 receptors in these cells.

Functional and structural effects of an Ala to Val mutation in the adenovirus serotype 2 fibre

H2ts125 is a fibre-defective, temperature-sensitive mutant of adenovirus serotype 2. H2ts125 fibre is unstable at the non-permissive temperature (ts phenotype), and does not migrate in the same way as the wild-type fibre in an SDS/polyacrylamide gel (elm phenotype). Sequence analysis has shown that H2ts125 carries two mutations on the fibre gene: Leu105 to Phe, and Ala434 to Val. Analysis of the structural modifications occurring in H2ts125 fibre was performed using peptide finger-printing and antipeptide sera as immunological probes. We found that all the detectable structural alterations in the mutant fibre were due to the substitution on codon 434. In addition, the ts phenotype was rescued by a wild-type DNA fragment containing the 3' moiety of the fibre gene and overlapping the 434th codon. Morphological analysis of fibre molecules observed under the electron microscope showed minor but statistically significant differences in the fibre length between mutant and wild-type. The mutant fibre was found to be slightly longer (308.8 +/- 1.9 A) than the wild-type fibre (300.1 +/- 2.1 A). Thus both ts and elm phenotypes were carried by the same Ala434 to Val mutation which probably resulted from a change in the three-dimensional structure of the fibre protein, and not from some proteolytic cleavage.

Role of early genes in pathogenesis of adenovirus pneumonia

Intranasal inoculation of type 5 adenovirus into the cotton rat Sigmodon hispidus produces a pneumonia pathologically similar to that in humans, and it, therefore, provides an excellent animal model to investigate the pathogenesis of this disease. The goal of this study was to test the hypothesis that accumulation of viral structural proteins is responsible for a major portion of the cell-damage-producing disease. Since viral DNA replication is essential for synthesis of the viral structural proteins, which are products of late genes, the hypothesis was tested using mutants defective in genes required for DNA synthesis. Most experiments were done with the conditionally lethal temperature-sensitive (ts) mutant H5ts125, which contains a mutation in the early region 2A (E2A) gene encoding the DNA-binding protein. The data show that infection with 1 x 10(9.0) plaque-forming units of H5ts125 induced a pneumonia that was as extensive and qualitatively the same as that after wild-type adenovirus type 5 infection, although H5ts125 did not replicate to produce infectious virus. When cotton rats were infected with 1 x 10(8.0) plaque-forming units of wild-type adenovirus type 5 or H5ts125, the pneumonias that followed were pathologically similar; in the latter phases, however, wild-type virus produced slightly more extensive pneumonia than did H5ts125, probably because its replication permitted infection of more susceptible cells.

O-linked GlcNAc in serotype-2 adenovirus fibre

Serotype-2 adenovirus fibre is shown to possess an O-linked GlcNAc residue and to have affinity for wheat germ agglutinin. The cytoplasmic and nuclear fibres are both glycosylated. Glycosylation seems to take place in the cytoplasm since most of the [14C]GlcN-labelled fibre is found in this compartment, little label being associated with the microsomes. Glycosylation of the fibre was not affected by inhibitors of N- and O-glycosylation. A variation in fibre glycosylation is observed among adenovirus. Among the serotypes tested, only serotype-5 adenovirus (another subgroup C virus) also incorporated [14C]GlcN into its fibre, but did not possess affinity for wheat-germ agglutinin. The GlcNAc is located in the N-terminal two-thirds of the fibre and more probably in the N-terminal one-third. The free or penton-base-associated fibres are similarly glycosylated. These results suggest that glycosylation is not involved in viral adsorption and in assembly with the capsid penton base. Thus, glycosylation might be a characteristic feature of subgroup C viruses.

Suppression of matrix protein synthesis by herpes simplex virus type 1 in human endothelial cells

The synthesis of matrix proteins was investigated in cultures of human umbilical vein endothelial cells (EC) infected with herpes simplex virus type 1 (HSV-1). EC cultures were either mock-infected or infected for 1 hour at a multiplicity of infection (MOI) of 5 or 20 infectious particles per cell. Synthesis was followed by determining [14C]-proline or [35S]-methionine incorporation into non-dialyzable proteins. Using SDS-PAGE we observed that synthesis of fibronectin (FN), type IV procollagen and thrombospondin (TSP) was inhibited in infected cultures as early as 2 hours becoming almost complete by 15 hours post-infection. The degree of inhibition of matrix protein synthesis was dependent on the dose of the virus inoculum (MOI 20 greater than MOI 5) and varied with the particular matrix protein, i.e. shut-off of type IV collagen occurred first followed by that of FN and then TSP. Pulse-chase experiments suggest that the absence of labeled matrix protein in the medium of infected cultures is not due to accumulation of protein within the infected cells since there was an equal and parallel reduction in the cell layer. Suppression of matrix proteins in infected cultures was confirmed by measuring the level of FN and TSP in uninfected and infected cultures in an enzyme-linked immunosorbent assay (ELISA). The three proteins were identified by ELISA, electroimmunoblot, immunoprecipitation and ion-exchange chromatography. The data suggest that HSV-1 infection of human EC suppresses matrix protein synthesis; the degree and time of complete shut-off varies with the protein and the virus dose.

Evidence for the existence of a thermolabile element in adenovirus type 5 that plays a role during an early stage of infection

In an attempt to learn the molecular mechanism behind the initial steps (before genome expression) of adenovirus infection, the effect of temperature treatment of adenovirus type 5 particles on their infectivity was studied. It was found that adenovirus type 5 could be inactivated by temperature treatment at between 43 and 44 degrees C. Both biochemical and biophysical examination of adenovirus particles failed to disclose any significant changes after exposure to temperatures up to 45 degrees C. Further, viral particles treated with the same temperature range retained their ability to attach to cell surface receptors and to penetrate the plasma membrane. Application of a temperature pulse of 44 degrees C to adenovirus-infected HeLa cells indicates that the infection can be inhibited by exposure of infected cells to a brief temperature pulse of 44 degrees C between 10 and 50 min postadsorption with a mid-point of 30 min postadsorption. In addition, electron microscopic examination of HeLa cells following a temperature pulse of 44 degrees C suggests that there is a failure to accumulate viral particles at the perinuclear region. These findings support the hypothesis that adenovirus contains a thermolabile element which plays a crucial role during an early stage of infection. Possible correlation of this element with the adenovirus endogenous protein kinase is also examined and discussed.

Inhibition of host cellular ribonucleic acid synthesis by glycoprotein of mumps virus

After infection with mumps virus, cellular ribonucleic acid synthesis of a murine lymphoma cell line, EL4, was appreciably depressed. The inactivation of viral infectivity by ultraviolet irradiation or the treatment of cells with mouse interferon did not abolish the inhibiting effect, suggesting that virus replication is not required for the depressed RNA synthesis. Envelope glycoproteins isolated from disrupted mumps virus caused inhibition of cellular RNA synthesis. The addition of low concentrations of specific antibody enhanced the inhibitory effect, probably through the formation of aggregates of glycoproteins. On the contrary, the glycoproteins showed no effect on RNA synthesis in the presence of cytochalasin D.

Herpes simplex virus types 1 and 2 induce shutoff of host protein synthesis by different mechanisms in Friend erythroleukemia cells

Herpes simplex virus type 1 (HSV-1) and HSV-2 disrupt host protein synthesis after viral infection. We have treated both viral types with agents which prevent transcription of the viral genome and used these treated viruses to infect induced Friend erythroleukemia cells. By measuring the changes in globin synthesis after infection, we have determined whether expression of the viral genome precedes the shutoff of host protein synthesis or whether the inhibitor molecule enters the cells as part of the virion. HSV-2-induced shutoff of host protein synthesis was insensitive to the effects of shortwave (254-nm) UV light and actinomycin D. Both of the treatments inhibited HSV-1-induced host protein shutoff. Likewise, treatment of HSV-1 with the cross-linking agent 4,5',8-trimethylpsoralen and longwave (360-nm) UV light prevented HSV-1 from inhibiting cellular protein synthesis. Treatment of HSV-2 with 4,5',8-trimethylpsoralen did not affect the ability of the virus to interfere with host protein synthesis, except at the highest doses of longwave UV light. It was determined that the highest longwave UV dosage damaged the HSV-2 virion as well as cross-linking the viral DNA. The results suggest that HSV-2 uses a virion-associated component to inhibit host protein synthesis and that HSV-1 requires the expression of the viral genome to cause cellular protein synthesis shutoff.

Purification and preliminary immunological characterization of the type 5 adenovirus, nonstructural 100,000-dalton protein

The nonstructural 100,000-dalton (100K) protein of type 5 adenovirus was isolated and purified from infected KB cells by a combination of ion-exchange and affinity chromatographies. Rabbit antiserum containing specific 100K protein antibodies was used for indirect immunofluorescence examination of cells infected with wild-type virus, 100K mutants, and hexon mutants. The 100K protein, which is synthesized as a late protein, was observed primarily in the cytoplasm of cells infected with wild-type and mutant viruses.

Requirement of protein synthesis for the degradation of host mRNA in Friend erythroleukemia cells infected wtih herpes simplex virus type 1

We describe experiments which demonstrate that shortly after infection of Friend erythroleukemia cells with herpes simplex virus (HSV), polyribosomes dissociate and cellular mRNA degrades. Analysis of infected cell extracts on sucrose density gradients demonstrates that the majority of the polyribosomes have dissociated to monoribosomes at 2 h postinfection. Physical measurements of infected-cell RNAs support this conclusion and demonstrate that the polyadenylated RNAs decrease in size. The degradation of mRNA is apparently a stochastic process as judged by the failure to detect a shift in the Crt1/2 when polyadenylated RNA extracted from infected cells at different times is hybridized to globin complementary DNA. In experiments designed to determine whether dissociation of polyribosomes is sufficient to cause degradation of globin mRNA, the amount of globin mRNA in uninfected cells did not change when cells were treated with NaF or pactamycin at concentrations sufficient to dissociate all polyribosomes. In cells infected with UV-irradiated virus polyribosomes dissociate but globin mRNA does not degrade, suggesting that it is possible to separate dissociation from degradation.

Alterations in the protein synthetic apparatus of Friend erythroleukemia cells infected with vesicular stomatitis virus or herpes simplex virus

We have compared the effects of infection with herpes simplex virus (HSV) and vesicular stomatitis virus (VSV) on the protein synthetic apparatus of Friend erythroleukemia cells. Previous studies demonstrated that infection with HSV rapidly shuts off the synthesis of globin and other cellular polypeptides (Y. Nischioka and S. Silverstein, 1977, Proc. Natl. Acad. Sci. U.S.A. 74: 2370-2374). In contrast to these findings, globin synthesis persists in Friend erythroleukemia cells infected with VSV. Physical measurements of the size of bulk-infected cell mRNA, using hybridization with polyuridylic acid, demonstrated that there was no detectable change in the size of mRNA's after infection with VSV. A comparison of the kinetics of hybridization of cytoplasmic RNA extracted from cells infected with either HSV or VSV with globin complementary DNA revealed that by 4 h postinfection with HSV only about 15% of the globin mRNA sequences remained, whereas there was no discernible change in the sequence abundance of globin mRNA in VSV-infected cells.

Degradation of cellular mRNA during infection by herpes simplex virus

The fate of preexisting mRNA sequences was examined after infection by herpes simplex virus. Murine erythroid cells transformed by Friend leukemia virus were used as the host. Such cells, when exposed to 2% dimethyl sulfoxide, produce large amounts of globin and globin mRNA. The protein and its mRNA are easily recognized at 4 days by electrophoresis in high percentage acrylamide gels and by hybridization to cDNA, respectively. Herpes simplex virus replicates in these cells. By 2 hr after infection the rate of protein synthesis decreases to 30% of the level in mock-infected cells and only 49+/-8% (SEM) of the globin mRNA sequences present prior to infection could be detected by hybridization to cDNA. At 4 hr after infection, when the rate of protein synthesis in infected cells is at a maximum, only about 15% of the globin mRNA sequences remained. Control experiments support the hypothesis that globin mRNA sequences are degraded after infection by herpes simplex virus.

Characterization of a temperature-sensitive mutant of human adenovirus type 7

The properties of a naturally occurring temperature-sensitive (ts) mutant of human adenovirus type 7 (Ad7) were studied. Mutant Ad7 (19), or E46-, was the nonhybrid adenovirus component derived from the defective simian virus 40 (SV40)-Ad7 hybrid (PARA). Growth of the mutant was restricted at 40.5 degrees C, and the ratios of virus yields in KB cells at 40.5 and 33 degrees C were 10(-2) to 10(-3). Viral DNA synthesis and the synthesis of adenovirus-specific antigens (tumor, capsid, hexon, and penton antigens) appeared normal at the restrictive temperature. The assembly of virus particles was aberrant, as determined by thin-section of infected cells. The infectivity of mutant virions was heat labile at 50 degrees C, suggesting a ts defect in a structural component of the viron. Analysis by polyacrylamide gel electrophoresis of [35S]methionine-labeled polypeptides synthesized in mutant-infected cells suggested that at least the major virion polypeptides were synthesized at the restrictive temperature. A lack of inhibition of host protein synthesis late in mutant infections, as compared with wild-type (WT) infections at both the permissive and nonpermissive temperatures, made quantitation of infected-cell polypeptides difficult. Analysis of the assembly of capsomeres from cytoplasmic extracts of infected cells on sucrose gradients and by non-dissociating polyacrylamide gel electrophoresis suggested that hexon capsomeres were made at 40.5 degrees C. The hexon capsomeres made by the mutant at either 33 or 40.5 degrees C displayed a decreased migration in the non-dissociating gels compared with the WT hexon capsomeres. The molecular weights of the mutant and WT hexon polypeptides were identical. These results suggest that the ts lesion of this group B human Ad7 mutant may be reflected in altered hexons. The mutant Ad7 interfered with the replication of adenovirus types 2 and 21 at the elevated temperature.

Interactions of KB-cell glycoproteins with an adenovirus capsid protein

Glycoprotein material extracted from human KB cells with a flurocarbon, trichlorotrifluoroethane (Arklone P), into a waste-soluble fraction binds to fibre, a structural protein of the adenovirus type-5 capsid. The fibre-binding glycoprotein(s) were purified by ion-exchange chromatography on DEAE-Sephadex and affinity chromatography on a fibre-Sepharose support. The purification procedure also includes a trypsinization step which eliminates the bulk of contaminating KB cell proteins present in the aqueous fraction without appreciably affecting the activity of the fibre-binding glycoprotein(s). Some comparison is made of the membrane-bound receptors for adenovirus and the water-soluble fibre-binding glycoprotein(s).

Hexon peptides of type 2, 3, and 5 adenoviruses and their relationship to hexon structure

Peptides of hexons from type 2 and 5 (subgroup III) and type 3 (subgroup I) adenoviruses were produced by treatment with cyanogen bromide and were separated by isoelectric focusing in polyacrylamide gels containing 8 M urea. Peptides with identical isoelectric points, but from different hexon types, were considered to have structural similarities. According to this criterion for chemical relatedness, about two-thirds of the type 2 and 5 hexon peptides may be considered similar. In contrast, the majority of the type 3 hexon peptides differed chemically from peptides of type 2 and 5 hexons. Virions and free hexons were iodinated with 125-I in the presence of lactoperoxidase and H-2-O-2. When 125-I-labeled virions were disrupted and the hexon was purified, the highly labeled cyanogen bromide peptides were labeled. When purified hexons from the excess cellular pool were iodinated, peptides common to types 2, 3, and 5 (peptides 12 and 14) were most extensively labeled. Thus, hexons assembled in virions and those free in solution were iodinated differently. The data suggest that immunologically the hexons in viral capsids react differently from unassembled hexons because the polypeptide chains assume slightly different folding configurations in the two hexon forms and therefore expose different regions of the protein to antibodies.

Characterization of type 5 adenovirus fiber protein

Type 5 adenovirus fiber protein was purified and subjected to chemical characterization. Equilibrium sedimentation ultracentrifugation analysis indicated that the intact fiber has a molecular weight of approximately 183,000. Denaturation and chemical analyses implied that the fiber consists of three polypeptide chains, each of about 61,000 mol wt. Mapping of tryptic peptides and electrophoretic separation of the constituent chains suggested that the intact fiber consists of two identical and one unique polypeptide chains.

How do viruses multiply?

This review article describes the mechanism of multiplication of viruses. Virus infection of mammalian cells proceeds in 4 main stages, adsorption of the virus to the host cell followed by penetration, pre-emption of the synthetic machinery of the cell by the virus, synthesis of viral macromolecular components under the direction of the viral genome, and assembly of viral components to produce mature virus progeny.

Induction of cellular DNA synthesis by the nondefective Adenovirus 2-Simian virus 40 hybrid viruses

Induction of cellular DNA synthesis by the nondefective adenovirus 2-simian virus 40 hybrid viruses was examined in monkey and hamster cells. It was not possible to discriminate the effects of the hybrid viruses from those of wild-type adenovirus 2.

Preparation and properties of an inhibitory extract from frog virus 3 particles

The structural constituents of the frog virus 3 particle were solubilized by treatment with a nonionic detergent followed by the addition of a high salt concentration. This soluble viral extract (SVE) inhibits host nucleic acid synthesis. Its activity on RNA synthesis was studied in KB cells and found to be dependent on the presence of DEAE dextran. Inactivation of the inhibitory properties of SVE were obtained by trypsin digestion, treatment with urea, or heat denaturation. Neutralization of the activity of SVE was obtained by anti-frog virus 3 serum but not by anti-BHK serum. In vitro a complex may be formed between polynucleotides and the inhibitor indicating a possible mechanism for vivo inhibition.

Transient inhibition of polyoma virus synthesis by sendai virus (parainfluenza I). II. Mechanism of the interference by inactivated virus

The mechanism of the transient inhibition of polyoma virus synthesis by betapropiolactone-inactivated Sendai virus was studied. Polyoma virus early functions did not appear to be affected, although deoxyribonucleic acid (DNA) and structural protein synthesis were inhibited 60 and 35% respectively. The inhibition of macromolecular synthesis was not sufficient to account for the 90% inhibition of infectious progeny formation. Encapsidation of polyoma DNA into mature virions appears to be completely inhibited after superinfection by beta-propiolactone-inactivated Sendai virus. Ultraviolet irradiation of live or beta-propiolactone-inactivated Sendai virus preparations abolishes the interfering capacity, indicating that a functional Sendai virus ribonucleic acid molecule is the interfering component.

Transient inhibition of polyoma virus synthesis by Sendai virus (parainfluenza I). I. Demonstration and nature of the inhibition by inactivated virus

Superinfection of polyoma virus-infected mouse embryo cells by beta-propiolactone-inactivated Sendai virus resulted in a 90% inhibition of the synthesis of infectious polyoma progeny. The interference is dependent upon the time of superinfection and the concentration of the inactivated virus. The inhibition of polyoma virus synthesis is transient in nature since normal synthesis of polyoma progeny virus is seen upon prolonged incubation. Interferon does not appear to be implicated in the interference. Various aspects of the biological and synthetic capabilities of beta-propiolactone-inactivated Sendai virus are also described.

Selection and preliminary characterization of temperature-sensitive mutants of type 5 adenovirus

Eight temperature-sensitive (ts) mutants that replicate normally at 32 C but poorly, if at all, at 39.5 C have been isolated from mutagenized stocks of a wild-type strain of type 5 adenovirus. Three mutagens were employed: nitrous acid, hydroxylamine, and nitrosoguanidine. Ts mutants were isolated from mutagenized viral stocks with frequencies between 0.01 and 0.1%. All eight mutants had reversion frequencies of 10(-5) or less. Complementation experiments in doubly infected cultures at the nonpermissive temperature separated the mutants into three nonoverlapping complementation groups. Complementation yields ranged from a 2.3- to a 3,000-fold increase over the sums of the yields from the two singly infected controls. Genetic recombination was also demonstrated; approximate recombination frequencies ranged from 0.1 to 15%. Preliminary biochemical and immunological characterization of the mutants indicated that: (i) the single mutant in complementation group I did not replicate its deoxyribonucleic acid (DNA) or synthesize late proteins at the nonpermissive temperature but did inhibit host DNA synthesis to 25% of an uninfected control; (ii) the four group II mutants replicated viral DNA, shut off host DNA synthesis, synthesized penton base and fiber, but did not synthesize immunologically detectable hexon; the three mutants in complementation group III synthesized viral DNA, shut off host DNA synthesis, and made immunologically reactive capsid proteins (hexon, penton base, and fiber).

Synthesis in vitro of type 5 adenovirus capsid proteins

Reaction mixtures containing cytoplasmic extracts and ribosomal fractions prepared from KB cells infected with type 5 adenovirus were able to carry out incorporation of amino acids into protein. The in vitro product included proteins which reacted specifically with antisera to adenovirus capsid proteins; in control experiments with extracts from uninfected cells, no reactions with the antisera were found. The viral proteins were synthesized in vitro on small polyribosomes, were released from them, and significant numbers of the free polypeptides were assembled in vitro into multimeric adenovirus capsid structures.