A domain of the hepadnavirus capsid protein is specifically required for DNA maturation and virus assembly

Mutations introduced into the capsid gene of duck hepatitis B virus (DHBV) were tested for their effects on viral DNA synthesis and assembly of enveloped viruses. Four classes of mutant phenotypes were observed among a series of deletions of covering the 3' end of the capsid open reading frame. Class I mutant capsids were able to support normal single-stranded and relaxed circular viral DNA synthesis; class II mutant capsids supported normal single-stranded DNA synthesis but not relaxed circular DNA synthesis; class III mutant capsids resembled class II capsids, but viral DNA synthesis was inhibited 5- to 10-fold; and class IV capsids were severely restricted in their ability to support viral DNA synthesis. Class I capsids were assembled into enveloped virions, but class II, III, and IV capsids were not. Viral DNA synthesized inside class II capsids was normal with respect to minus-strand DNA initiation, plus-strand DNA initiation, and circularization of the DNA, but plus strands failed to be elongated to mature 3-kb DNA. The results suggest that a function of the capsid protein specifically required for viral DNA maturation is also required for assembly of nucleocapsids into envelopes. Thus, class II mutants appear to be defective in the appearance of the "packaging signal" for virus assembly (J. Summers and W. Mason, Cell 29:403-415, 1982).

Asset disposal: follow company policies or follow the law?

Several ethical issues can arise in disposing of assets. The proper management of these issues involves awareness of the applicable laws and development of policies and enforcement that respect those laws. Several examples of appropriate policy, following classical management principles, served to document the points under discussion.

Demographics, strategic planning, and marketing: a low budget approach

Health care organizations with constrained planning budgets can access data sources which will be of great assistance in strategic and market analysis. The data described in this article can be obtained for $250 or less. For segmenting the market even further, down to the International Classification of Disease (ICD)-9 Code Level, the National Center for Health Statistics of the Department of Health and Human Services publishes an annual data book which indicates the use rates for every ICD-9 Code. This extremely valuable data source is all less than $10. Managers can take inexpensive data from the Census and from HHS and proceed to determine major opportunities and challenges facing their institutions. The same data then serve as the basis for planning about how to meet those challenges or take advantage of those opportunities. Finally, the same data will allow product line management to proceed on the basis of quantitative goals that are established in terms of the actual facts of the local situation. The skills required to perform these analyses are not complex, but the task is time intense.

Hepadnavirus envelope proteins regulate covalently closed circular DNA amplification

Primary duck hepatocytes were infected with a mutant duck hepatitis B virus defective in envelope protein but competent for viral DNA synthesis. Cells infected by this mutant accumulated higher levels of viral covalently closed, circular DNA (cccDNA) than those infected by wild-type virus. The accumulation of high levels of cccDNA was due to a failure of the mutant-infected cells to suppress de novo cccDNA synthesis compared with suppression by cells infected by the wild type. The envelope-defective virus failed to establish a persistent infection in vitro, possibly because of a virus-mediated cell death. Therefore, one or both viral envelope proteins are required for regulation of cccDNA synthesis and for maintenance of persistent infection in vitro.

In hepatocytes infected with duck hepatitis B virus, the template for viral RNA synthesis is amplified by an intracellular pathway

During the productive phase of chronic hepadnaviral infections, virion DNA synthesis occurs in the cytoplasm of the infected hepatocyte, but viral RNA is synthesized in the nucleus, apparently from a covalently closed, circular (CCC) viral DNA. J. Tuttleman, C. Pourcel, and J. Summers (1986a, Cell 47, 451-460) have shown that the intracellular levels of CCC DNA can increase during initiation of infection of duck hepatocytes in vitro with duck hepatitis B virus and during long term culture of infected duck hepatocytes in vitro. This amplification of CCC DNA occurs through the reverse transcription pathway. To distinguish between an entirely intracellular process of amplification and amplification due to multiple infections by extracellular virus in the virus producing cultures, suramin was added to the infected cultures to block superinfection. We found that CCC DNA amplification occurred at least as efficiently in the presence of suramin as in its absence. First, there was a net increase in the total amount of CCC DNA in the cultures both in the presence and in the absence of suramin. Second, synthesis of CCC DNA in the presence and absence of suramin was observed by density labeling of this viral DNA by growth of the cultures in medium containing BUdR. Amplification was also demonstrable in the presence of neutralizing duck antibodies. These results support the hypothesis of Tuttleman et al. (1986a) that CCC DNA amplification in chronically infected cultures and, by inference, the mechanism of persistent infection involves primarily intracellular regulatory mechanisms.

Synthesis of hepadnavirus particles that contain replication-defective duck hepatitis B virus genomes in cultured HuH7 cells

To evaluate the possibility of producing transducible replication-defective hepadnaviruses, cloned mutant duck hepatitis B virus genomes were tested both for virus antigen production and viral DNA synthesis following transfection into the human hepatoma cell line HuH7. Deletion of a cis-acting 12-nucleotide sequence implicated in viral DNA synthesis, direct repeat 1 (DR1), resulted in the loss of ability to synthesize both mature viral DNA and infectious virus. The delta DR1 mutant, however, produced envelope and core antigens and was shown to provide trans-acting functions required for the assembly of infection-competent particles. Thus, mutants with mutations in viral genes could be rescued as DNA-containing viral particles after cotransfection with delta DR1. The efficiency of rescue was influenced by the site of mutation. A mutant DNA encoding truncated core and envelope proteins not only was poorly rescued but also was able to suppress the production from a wild-type DNA of infectious virus.

In vitro infection of woodchuck hepatocytes with woodchuck hepatitis virus and ground squirrel hepatitis virus

Primary cultures of woodchuck hepatocytes were demonstrated to be susceptible to in vitro infection by both woodchuck hepatitis virus and ground squirrel hepatitis virus, as evidenced by the appearance of DNA species characteristic of hepadnavirus replication. Initiation of infection by woodchuck hepatitis virus was blocked by the presence of suramin, polybrene, or dideoxycytidine. Viral CCC DNA, the putative template for viral RNA transcription, was detected at 2 days postinfection. Accumulation of intracellular intermediates in virion DNA synthesis was negligible until 7-10 days postinfection, but these DNA intermediates then increased dramatically in amount over the next few weeks. Results were obtained which suggested that the prolonged accumulation of intermediates in virion DNA synthesis was an intrinsic property of the infection of individual cells, and not the result of a slow spread of virus through the cultures.

Role of thromboxane A2 as a mediator of platelet-activating-factor-induced aggregation of human platelets

1. At present it is unclear whether platelet-activating-factor (PAF)-induced aggregation is mediated by thromboxane. To obtain further information about this event we have compared the affects of aspirin on platelet aggregation and secretion induced by PAF and collagen. 2. Collagen and PAF induced aggregation and secretion in human platelets in a dose-related manner. 3. Aspirin inhibited the magnitude of both platelet aggregation and secretion induced by PAF and collagen, but the degree of inhibition was much greater for collagen. 4. Aspirin strongly inhibited the aggregation rate of collagen-induced platelet aggregation, but had no measurable effect on the rate of PAF-induced aggregation. 5. Inconsistencies reported in previous studies of the effect of aspirin on PAF-induced platelet aggregation may be explained, in part, by the doses of PAF used and the method of inactivating cyclo-oxygenase (in vitro compared with in vivo). 6. Our results suggest that the initial events of PAF-induced aggregation are independent of thromboxane A2 formation and that thromboxane A2 plays only a minor role in the later phase of PAF-induced aggregation.

Determining your duties

This issue's discussion has two goals. First, we shall examine the reasons clinical personnel gravitate to the Kantian concept of duty. Second, we shall examine a technique used within Kantian theory that will help you decide when an ethical dilemma obligates you to act regardless of the consequences.

Characterization of the major duck hepatitis B virus core particle protein

The amino acid composition of the major duck hepatitis B virus (DHBV) core particle proteins was determined. The results of this analysis indicated that cores are composed of a single major protein that initiates translation from the second available AUG in the DHBV core gene. Proteins isolated from core particles purified from the cytoplasm of DHBV-infected duck hepatocytes exhibited heterogeneity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, independent of the stage of viral DNA maturation. Incubation of native cores with alkaline phosphatase removed this heterogeneity, indicating that phosphorylation of external amino acids was responsible. Core protein isolated from mature DHBV purified from serum of infected animals did not display heterogeneity, suggesting a possible role for dephosphorylation in virus maturation.

Duck hepatitis B virus (DHBV) particles produced by transient expression of DHBV DNA in a human hepatoma cell line are infectious in vitro

Transfection of the human hepatocellular carcinoma cell line HuH7 with a plasmid containing a tandem copy of the duck hepatitis B virus DNA sequence resulted in transient replication of the virus. Viral particles secreted by transfected HuH7 cells exhibited physical properties similar to those of serum-derived duck hepatitis B virus and were infectious in primary duck hepatocyte cultures.

Characterization of a herpesvirus isolated from woodchuck hepatocytes

A DNA virus with the characteristics of a herpesvirus has been isolated from woodchuck hepatocytes cultured in vitro. We refer to this virus as herpesvirus of marmots (HVM). Electron microscopy of thin sections of HVM-infected cells showed nucleocapsids with a hexagonal outline and a diameter of 80 nm. Enveloped virions were seen in cytoplasmic vacuoles and outside the cell. Negatively stained virus particles purified from cell supernatants were enveloped with the characteristic appearance of herpesviruses. The DNA was double-stranded with a molecular size of approximately 140 kb and a G + C content of 73%. The virus replicated with a lytic effect in kidney cells of owl monkeys and African green monkeys, baby hamster kidney cells, feline kidney cells and WCH-17, a cell line derived from a woodchuck hepatoma. An indirect immunofluorescence assay has shown the presence of antibody to HVM in seven out of 37 animals tested. An important reason for studying HVM lies in its possible role in infection or the disease produced by woodchuck hepatitis virus, an animal model for human hepatitis B virus.

A simple, cost-effective method for determination of entrance skin exposure for diagnostic radiology examinations

We devised a simple method using inexpensive instrumentation for determination of accurate levels of radiation exposure. The method can be used by technologists in small hospitals, private practices, and other facilities that do not employ full-time or consulting physicists to provide these data.

Replication of human hepatitis delta virus in primary cultures of woodchuck hepatocytes

We obtained two lines of evidence that monolayer cultures of primary woodchuck hepatocytes support replication of the genome of human hepatitis delta virus (HDV). (i) From a Northern (RNA blot) analysis of the HDV-related RNA in infected cultures, both genomic and antigenomic 1.7-kilobase RNA species were detected at 11 days after infection. The ratio of genomic RNA to antigenomic RNA was 2:1 to 10:1, comparable to that previously reported in studies of experimentally infected chimpanzees and woodchucks. (ii) Replication in culture was also demonstrated by in situ hybridization with a strand-specific probe. Such studies showed that only a small fraction of the cultured cells supported replication and that in such cells the relative and absolute levels of the HDV RNAs were comparable to those in liver cells infected in vivo. Furthermore, as with the in vivo studies, the HDV RNAs were predominantly localized to the nucleus. In summary, we demonstrated that cultured cells supported both the early events of HDV adsorption and penetration and the intermediate events of genome replication.

Formation of the pool of covalently closed circular viral DNA in hepadnavirus-infected cells

Covalently closed circular (CCC) double-stranded DNA believed to be the transcriptional template for duck hepatitis B virus (DHBV) is amplified in aging primary cultures of hepatocytes from congenitally infected ducklings. Analysis of 5-bromodeoxyuridine-labeled heavy/light CCC DNA shows that the relaxed circular DNA synthesized in the cytoplasm by reverse transcription is the predominant precursor to the amplified pool of nuclear viral CCC DNA. In vitro infection of uninfected hepatocyte cultures with DHBV demonstrates that a similar 50-fold amplification of CCC DNA occurs during an early stage in the infection before virus production. This amplification allows the establishment of a pool of transcriptional templates in the cell without the need for semiconservative replication or multiple rounds of infection. This process may account for the ability of hepadnavirus-infected cells persistently to produce virus particles in the absence of stable integration of viral DNA.

Providing indigent care: strategic issues in management, marketing and ethics

Uncompensated cares poses considerable management, marketing and ethical challenges to health care managers. A variety of responses are examined which offer the possibility of reducing the need for inpatient care and the cost of that care as well as for the enhancement of the organization's positioning in the marketing and sales environment. Some of the programs will require support from local community agencies or employers, but others will be quite feasible without such support. Additionally, the programs build on sensitivity to the hospital mission as opposed to turning away from it.

Right ventricular failure and ascites in broiler chickens caused by phosphorus-deficient diets

Phosphorus-deficient diets fed to broiler chicks from day 1 to day 21 induced rickets. Some chicks were stunted, but most grew well, though they had increased respiratory rates, high arterial carbon dioxide partial pressure, and low oxygen partial pressure and were polycythemic. Most of the broilers that died showed signs of pulmocardiovascular abnormalities, some died from hypoxia, and some died from right ventricular failure with or without ascites. Many broilers had mild to marked right ventricular hypertrophy and dilation with or without ascites when examined at 21 days. It is suggested that right ventricular hypertrophy and dilation was a response to pulmonary arterial hypertension caused by chronic hypoxia, which resulted from inability to breathe normally because of poor rib strength and infolding. When right ventricular failure occurred, it was secondary to right ventricular hypertrophy and dilation.