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Biomedical subjects

G Ju

Publications and source records attributed to G Ju.

At least 145 records · Page 8Linked to original sources
PubMed1983

Endogenous avian retroviruses contain deficient promoter and leader sequences.

A sensitive and quantitative biological assay has been utilized to measure the ability of the exogenous and endogenous avian retroviral long terminal repeats (LTR) to promote gene expression in avian cells. This assay has revealed that the exogenous virus RAV-2 LTR is approximately equal to 10-fold more active than the LTRs of endogenous viruses RAV-0, ev-1, and ev-2. The endogenous viral LTRs show approximately equal activity. Upstream flanking cellular or viral sequences have no significant modulating effect on gene expression in our assay. Unexpectedly, we have detected and localized an additional defect outside of the LTR in the 5' noncoding leader sequence of ev-1 that further decreases gene expression relative to RAV-0 by approximately equal to 10-fold.

Animals↗
PubMed1983

Viral sequences determining the oncogenicity of avian leukosis viruses.

Our analyses of the sequence of the recombinant virus NTRE7 and comparison with its endogenous and exogenous ALV parents indicate that a section of approximately 400 base pairs at the 3' end of the genome encodes a function which is required for oncogenicity. This section includes an exogenous virus specific region (XSR) of approximately 148 base pairs and the U3 region of the LTR. At present it seems most likely that the function required for oncogenicity is the transcription promoter contained in the U3 region. Assays designed to measure promoter activity of endogenous and exogenous LTRs show a 10 fold difference between the two. This result is consistent with the notion that RAV-0 is non-oncogenic because its promoter activity falls below the limit required for oncogene activation. Our findings suggest that there may be a critical threshold for oncogene activation for which the RAV-2 value represents an upper limit.

Animals↗
PubMed1982

Molecular analysis of the c-myc locus in normal tissue and in avian leukosis virus-induced lymphomas.

We isolated molecular clones of the provirus-host cell junctions (tumor junction fragments) from two avian leukosis virus-induced lymphomas and compared the structures of these clones with a clone of the normal c-myc gene. Restriction mapping and DNA sequencing demonstrated that normal proviral integration events occurred adjacent to c-myc in both tumors, without gross structural alteration of c-myc. The right long terminal repeat of an avian leukosis virus provirus is integrated upstream from the bulk of the c-myc coding sequences and oriented such that transcription can initiate within the long terminal repeat and proceed downstream into c-myc. A comparison of a tumor junction fragment with the v-myc gene showed that there are two regions of v-myc-related sequences (which are probably exons) separated by 1 kilobase of sequences unrelated to v-myc (probably an intron). A DNA sequence analysis of the tumor junction fragments suggested that integration had occurred in exons adjacent to splice donor sites. This suggests that there are additional exons and introns in c-myc. Based on these findings, a model is proposed for the genesis of the tumor-specific RNAs containing viral-5' and c-myc information in avian leukosis virus-induced lymphomas.

Animals↗
PubMed1982

Nucleotide sequence analysis of avian retroviruses: structural similarities with transposable elements.

Integrated retroviral genomes are flanked by direct repeats of sequences derived from the termini of the viral RNA genome. These sequences are designated long terminal repeats (LTRs). We have determined and analyzed the nucleotide sequence of the LTRs from several exogenous and endogenous avian retroviruses. These LTRs possess several structural similarities with eukaryotic and prokaryotic transposable elements: 1) inverted complementary repeats at the termini, 2) deletions of sequences adjacent to the LTR, 3) small duplications of host sequences flanking the integrated provirus, and 4) sequence homologies with transposable and other genetic elements. These observations suggest that LTRs function in the integration and perhaps transposition of retrovirus genomes. Evidence exists for the presence of a strong promoter sequence within the LTR. The retroviral LTR also contains a "Hogness box" up-stream of the capping site and a poly(A) signal. These features suggest an additional role for the LTR in the regulation of gene expression.

Animals↗
PubMed1981

Biological activity of cloned retroviral DNA in microinjected cells.

Avian retroviral DNA molecules that had been cloned from infected cells by using recombinant DNA techniques were microinjected into either uninfected chicken embryo fibroblasts (CEF) or CEF transformed by the envelope glycoprotein-deficient Bryan strain of Rous sarcoma virus [RSV(--)cells]. Retroviral DNA injected into RSV(--) cells directed transcription of envelope mRNA, which was then able to complement the RSV(--) env deficiency and promote the production of infectious transforming virus. The retroviral DNA also directed the production of fully infectious virus after injection into uninfected cells or RSV(--) cells. Virus production began within 3--4 hr after microinjections. When 100 DNA molecules per cell were injected, almost all injected cells produced infectious virus. As the number of injected molecules per cell was decreased, a corresponding decrease was observed in the number of cells that produced infectious virus. DNA injected into the cytoplasm was 1/50th to 1/10th as effective in virus production as DNA molecules injected into the nucleus. DNA molecules containing one or two tandem copies of the viral long terminal repeat were equally effective in virus production.

Animals↗
PubMed1981

Comparison between the viral transforming gene (src) of recovered avian sarcoma virus and its cellular homolog.

Recovered avian sarcoma viruses are recombinants between transformation-defective mutants of Rous sarcoma virus and the chicken cellular gene homologous to the src gene of Rous sarcoma virus. We have constructed and analyzed molecular clones of viral deoxyribonucleic acid from recovered avian sarcoma virus and its transformation-competent progenitor, the Schmidt-Ruppin A strain of Rous sarcoma virus. A 2.0-megadalton EcoRI fragment containing the entire src gene from each of these clones was subcloned and characterized. These fragments were also used as probes to isolate recombinant phage clones containing the cellular counterpart of the viral src gene, termed cellular src, from a lambda library of chicken deoxyribonucleic acid. The structure of cellular src was analyzed by restriction endonuclease mapping and electron microscopy. Restriction endonuclease mapping revealed extensive similarity between the src regions of Rous sarcoma virus and recovered avian sarcoma virus, but striking differences between the viral src's and cellular src. Electron microscopic analysis of heteroduplexes between recovered virus src and cellular src revealed a 1.8-kilobase region of homology. In the cellular gene, the homologous region was interrupted by seven nonhomologous regions which we interpret to be intervening sequences. We estimate the minimum length of cellular src to be about 7.2 kilobases. These findings have implications concerning the mechanism of formation of recovered virus src and possibly other cell-derived retrovirus transforming genes.

Alpharetrovirus↗
PubMed1980

Nucleotide sequence analysis of the long terminal repeat (LTR) of avian retroviruses: structural similarities with transposable elements.

The nucleotide sequences of the long terminal repeat (LTR) from six independently derived avian retrovirus recombinant DNA clones have been determined. The LTRs from three clones are approximately 350 bp in length and differ only in minor base insertions or substitutions. Three other clones have smaller LTRs, each with a large deletion which ranged from 89 to 161 bp. Sequence comparisons of the six LTRs indicate that there is conservation of sequences derived from the 5' terminus of viral RNA and extensive divergence of the 3'-specific sequences. The LTR sequences were obtained from clones of unintegrated viral DNA. Comparison of these LTRs with the sequence of an integrated Schmidt-Ruppin D provirus deduced previously reveals that two nucleotides present at the terminus of the LTR of the unintegrated DNA are absent in the integrated provirus. Analysis of the nucleotide sequence of the LTR from one clone, lambda RAV2-2, reveals several putative regulatory sites for the initiation and termination of transcription. There are also several structural features of the LTR which are analogous to procaryotic and eucaryotic transposable elements. These structural analogies include the presence of inverted complementary repeats at the termini of the LTR, deletions adjacent to LTR termini, and sequence homologies with transposable and other genetic elements. These observations suggest that the LTR of retroviruses function in the control of gene expression and integration.

Avian Leukosis Virus↗
PubMed1980

Complementation analysis of measles virus mutants isolated from persistently infected lymphoblastoid cell lines.

Human lymphoblastoid cell lines persistently infected with measles virus release a heterogeneous population of virions. At least 80% of the infectious particles were temperature sensitive for plaque formation at 39 degrees C. Plaque-purified temperature-sensitive mutants from four persistently infected human lymphoblastoid cell lines were shown to be heterogeneous with respect to efficiency of plating at 31 and 39 degrees C, as well as to antigen and RNA production at 39 degrees C. The heterogeneity was confirmed by complementation analysis in which 21 temperature-sensitive isolates were found to represent at least four of the five previously described complementation groups of measles virus. Two isolates complemented four reference temperature-sensitive mutants. These isolates either represent new complementation groups or are members of the fifth complementation group, group E. The majority of isolates were found to have multiple mutations, and group B mutants (RNA-) predominated. Two temperature-sensitive isolates were able to interfere with production of parental measles virus at both permissive and nonpermissive temperatures.

Antigens, Viral↗
PubMed1980

Isolation and characterization of recombinant DNA clones of avian retroviruses: size heterogeneity and instability of the direct repeat.

Unintegrated proviral DNA of Schmidt-Ruppin B Rous sarcoma virus was cloned in the bacteriophage lambda vector Charon 21A. A total of 12 independent recombinant lambda SRBtd clones which were derived from the transformation-defective component in the viral preparation were analyzed with restriction endonucleases and molecular hybridization techniques. Three classes of clones were observed. Type I clones contained a 5.0-megadalton insert of viral DNA, type II clones contained phage with two size classes of inserts (5.0 and 5.2 megadaltons), and one type III clone contained only a 5.2-megadalton insert. The smaller insert present in type II clones appeared to be derived by deletion of one copy of a directly repeated sequence which was present in the larger insert. Mapping data indicated that the deletion includes all or part of the terminal repeat found in linear double-stranded proviral DNA. Similar results were obtained from lambda RAV2 recombinant clones derived from Rous-associated virus type 2. Analysis of DNA from type II and type III clones of lambda SRBtd and lambda RAV2 revealed limited heterogeneity in the size of the direct repeat.

Avian Leukosis Virus↗
PubMed1978

Isolation of a heterogeneous population of temperature-sensitive mutants of measles virus from persistently infected human lymphoblastoid cell lines.

Two human lymphoblastoid B-cell lines, WI-L2 and 8866, were infected with the Edmonston strain of measles virus at a multiplicity of infection of 10(-6), and stable persistent infections were established. By immunofluorescence and electron microscopy, the vast majority of cells from both cell lines were expressing viral antigens and releasing virion-like particles. However, very little infectious virus could be detected at 37 degrees C, either by an infectious centers assay or by titration of supernates from persistently infected cultures. When cultures were shifted to 31 degrees C, the cells released a population of virus that was temperature-sensitive. Clonal analysis of supernatant virus at 31 degrees C revealed a highly heterogeneous population of temperature-sensitive mutants, differing in plating efficiency ratios, thermolability, and antigen production at the nonpermissive temperature. Factors such as interferon, defective interfering particles, and extracellular virus do not appear to be important in maintaining the persistent carrier state. These studies have important implications for persistent infections of lymphoid cells in vivo, and the slow neurological diseases associated with measles, subacute sclerosing panencephalitis, and multiple sclerosis.

Antibodies, Viral↗
PubMedDate not supplied

Transcriptional interference in avian retroviruses--implications for the promoter insertion model of leukaemogenesis.

The downstream (3') long terminal repeat (LTR) of an avian retroviral provirus is unable to act as an efficient promoter of transcription when a transcriptionally active upstream (5') LTR is present. This transcriptional interference may explain the observation that only deleted proviruses have been observed inserted adjacent to c-myc in avian leukosis virus induced lymphomas of chickens.

Animals↗
PubMedDate not supplied

Plasticity of GAP-43 innervation of the spleen during immune response in the mouse. Evidence for axonal sprouting and redistribution of the nerve fibers.

The amount and distribution of growth-associated protein (GAP-43)-like immunoreactive nerve fibers in the spleen of normal and immunized BALB/c mice were studied using immunohistochemical methods. A significant increase in the amount, as well as redistribution and morphological changes, of the GAP-43-like immunoreactive nerve fibers occurred in PPD (purified protein derivative from tuberculin) immunized animals. In the control animals, the GAP-43-like immunoreactive nerve fibers were found mainly distributed in association with vascular plexuses, with minor extension into the parenchyma of the inner zone of the periarterial lymph sheath. In the immunized animals, in addition to denser vascular plexuses, more fibers appeared in the outer zone of the periarterial lymph sheath, the marginal zone, and the red pulp, all known to be the sites where immune responding lymphocytes are located. Furthermore, the nerve fibers tended to have more branches and bear richer varicosities. The results suggest that active nerve remolding takes place in the spleen during immune response, which may serve as a mechanism through which the nervous system regulates immune responses.

Animals↗