Biomedical subjects

S L Zeichner

Publications and source records attributed to S L Zeichner.

25 records · Page 2Linked to original sources

PubMed1991

Linker-scanning mutational analysis of the transcriptional activity of the human immunodeficiency virus type 1 long terminal repeat.

We have compared the relative importance of transcription regulatory regions in the U3 and R regions of the human immunodeficiency virus type 1 long terminal repeat (LTR) by using linker-scanning mutational analysis. Twenty-six mutant LTR-chloramphenicol acetyltransferase (CAT) transient expression plasmids were prepared in which consecutive 18-bp regions of wild-type LTR were replaced with an NdeI-XhoI-SalI (NXS) polylinker. The mutant LTR-CAT plasmids were transfected into unstimulated Jurkat cells, Jurkat cells stimulated with phytohemagglutinin and tetradecanoylphorbol acetate, and Jurkat cells which constitutively express the human immunodeficiency virus type 1 trans-activator protein, Tat. Transcriptional activity was measured by analysis of CAT activity. The activities of these mutants identified one major and several minor transcription control elements in addition to previously identified elements. In addition, this fine-structure analysis identified differences in utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells. A significant regulatory region was indicated by linker-scanning mutations between nucleotides -183 and -130 (relative to the transcription start site, +1). These mutations caused marked decreases in activity of the LTR in unstimulated and especially in stimulated Jurkat cells but had no effect in Tat-expressing Jurkat cells. DNA mobility shift studies comparing probes of wild-type and mutant sequences in the -183 to -130 region indicated that alterations in specific DNA binding correspond to the altered transcriptional activity of the mutants. The effects of mutations in several regulatory regions, in addition to the -183 to -130 region described above, differ between Tat-expressing and -nonexpressing Jurkat cells. For example, the NF-kB sites are necessary for transcription in both Tat-expressing and -nonexpressing cells. However, Tat-expressing Jurkat cells primarily require only the 3'-proximal site, while both stimulated and unstimulated Jurkat cells appear to require both sites. Mutants downstream of the TATA element cause a more significant decrease in activity in Tat-expressing Jurkat cells than in the others. Finally, several mutations in the 5' half of the LTR (-453 to -184) show modest increases in transcription (1.5-fold or less) in unstimulated Jurkat cells only, suggesting possible negative regulatory sites. In summary, our studies have identified a control region (-183 to -130) upstream of the NF-kB sites and have more precisely defined significant differences in the utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells.

Base Sequence↗

PubMed1991

Analysis of the human immunodeficiency virus long terminal repeat by in vitro transcription competition and linker scanning mutagenesis.

Previous studies designed to map the transcriptional regulatory sequences of the human immunodeficiency virus (HIV) long terminal repeat (LTR) have shown disparate results depending on the method of analysis. Experiments have shown that deletions 5' to -104 (relative to the transcription start site, +1) are not required for transcription in vitro, while other experiments have shown that various mutations in this 5' region of the HIV-1 LTR affect both reporter gene activity in transient expression systems and viral growth. To correlate in vitro and in vivo findings, we performed in vitro transcription competition studies to define minimal sequences necessary for competitive factor binding or competitive transcription complex formation. Using normal HeLa cell nuclear extracts, we found that transcription of a reporter gene run by the U3-R region was efficiently competed only by intact LTR DNA fragments representing virtually the entire U3-R region (-453 to +80). Smaller subfragments of the LTR were less effective competitors; these included fragments from -453 to -159, which had a modest competitive ability at higher competitor concentrations, -159 to +80, and -402 to -34, which were both relatively poor competitors. These findings indicate that although the U3-R region truncated to -104 is able to promote in vitro transcription, a more stable transcription complex appears to form on the entire U3-R region. Hence sequences between -453 and -104 appear to be significant in transcription complex formation. In vivo transfection competition studies confirmed these findings. Specific sequences between -453 and -104 which may affect expression or transcription complex formation were mapped using a set of linker-scanning mutants spanning the LTR.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1988

Mechanisms and pathways of congenital infections.

Fetal and neonatal infections can occur at different times during pregnancy, from conception to birth. Infections that take place near the time of conception often destroy the zygote or embryo and only rarely leave definitive evidence. The mother can transmit the infection to her fetus through several routes, but the most likely routes are through ascending infections and through the blood. The inability of most agents to infect the early embryo probably depends largely on local barriers to the infectious agent, such as the zona pellucida. Some viruses, however, because of their systems for gene regulation of expression, can infect only embryos of certain developmental stages. Certain retroviruses can infect embryos, integrate into cellular DNA, and become part of the germline. After implantation, most infectious agents reach the fetus hematogenously. Organisms circulating in the mother reach and infect the placenta. They then may breach the placenta, gain access to the fetal circulation, and disseminate through the fetal body. Agents with particular tropisms infect particular organs and cause particular symptom complexes. The damage done by the organisms depends largely on the gestational age of the fetus at the time of the infection. The ability of the agent to infect or damage the fetus at all often depends on whether the mother is experiencing a primary infection or has previously mounted an effective immune response. Agents harm the fetus through direct destruction of parenchymal cells, through destruction of blood vessels and resulting infarction, through continued replication in fetal and neonatal tissues, through altering the growth parameters of various fetal tissues, and through provoking autoimmune responses. Infections that begin in the perinatal period usually infect the fetus by direct inoculation from infected foci in the birth canal or through direct contact with large amounts of infected maternal body fluids. Direct tissue destruction of the immediate sequelae of invasive infections usually causes the fetal damage from these perinatally acquired agents. The clinical features of the disease that begin in this period provide an opportunity for effective therapeutic intervention. Understanding the routes of fetal infection and the mechanisms underlying fetal damage from infection will help in devising strategies for preventing and treating congenital infections.

Bacterial Infections↗

PubMed1983

Isolation and characterization of macrophage phagosomes containing infectious and heat-inactivated Chlamydia psittaci: two phagosomes with different intracellular behaviors.

Infectious Chlamydia psittaci enters macrophages via a cytochalasin B-insensitive pathway in which chlamydia-containing phagosomes do not fuse with lysosomes; heat-inactivated C. psittaci enters macrophages via a route in which phagosomes do fuse with lysosomes. In an attempt to explain these differences, phagosomes containing infectious and heated chlamydiae were isolated from mouse macrophages by a procedure developed to isolate L-cell chlamydial phagosomes by rate zonal centrifugation. Macrophage phagosomes acted similarly to L-cell phagosomes on dextran and discontinuous sucrose gradients and exhibited similar detergent sensitivities. Total proteins of the two phagosomes were compared with each other, L-cell proteins, and surface-labeled proteins from macrophages. Both macrophage phagosome membranes had at least nine proteins with equal sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobilities; some were the same as L-cell phagosome proteins. Each phagosome had at least one protein not seen in the other. Only two phagosome proteins had mobilities equal to macrophage plasma membrane proteins. Macrophage phagosomes containing infectious and heat-inactivated C. psittaci, although created by different entry mechanisms and destined for different intracellular fates, exhibited only a few differences in their proteins.

Animals↗

PubMed1982

Association between resistance to superinfection and patterns of surface protein labeling in mouse fibroblasts (L cells) persistently infected with Chlamydia psittaci.

When mouse fibroblasts (L cells) were persistently infected with Chlamydia psittaci strain 6BC, they became immune to superinfection because they no longer associated with exogenous C. psittaci in a way that led to ingestion and intracellular multiplication. At the same time, the persistently infected L cells also exhibited changes in surface structure as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiographic visualization of the surface-exposed plasma membrane proteins that had been labeled with 125I by lactoperoxidase-catalyzed iodination. The most prominent changes were the appearance of a highly labeled band with an apparent molecular weight of 35,000 and the generalized reduction in intensity of labeling of proteins migrating in the apparent molecular weight range of 60,000 to 100,000. Neither resistance to superinfection nor alteration in cell surface structure depended on the presence of visible chlamydial inclusions. When L cells were cured of persistent infection, either spontaneously or by treatment with chlortetracycline or rifampin, immunity to superinfection disappeared, and the patterns of surface-labeled proteins of the cured cells once again resembled the patterns of wild L cells. It was suggested that resistance to superinfection is the result of reversible changes in the structure of the putative host cell receptor for chlamydiae that are produced in some unknown way by the persistent chlamydial infection.

Animals↗

PubMed1982

Isolation and characterization of phagosomes containing Chlamydia psittaci from L cells.

The obligate intracellular procaryote Chlamydia psittaci enters host cells by a mechanism similar to, but distinct from, conventional phagocytosis. To better understand chlamydial uptake, L-cell phagosomes containing a single chlamydial cell were isolated and studied. Two rounds of dextran rate-zonal gradient centrifugation of L cells homogenized 1 h after infection with C. psittaci yielded phagosomes relatively free of other membranous structures. In double-label experiments, the phagosomes were enriched over 40-fold for radioactivity derived from chlamydiae as compared with the initial homogenate. Several lines of evidence showed that the structures isolated on dextran gradients were chlamydial phagosomes. These structures and free chlamydiae banded at different positions on discontinuous sucrose gradients. The difference was destroyed by the nonionic detergent Nonidet P-40, which disrupts plasma membranes but has no effect on C. psittaci. Material labeled on the surface of the L-cell plasma membrane cosedimented with the phagosome fractions. Electron microscopy of these fractions revealed structures having the appearance of a chlamydial elementary body surrounded by a unit membrane. Sodium dodecyl sulfate-polyacrylamide gels of the phagosome membranes displayed 10 major protein bands, less than the total number of surface-labeled proteins in the L-cell plasma membrane. Seven of the proteins of phagosome membranes had electrophoretic mobilities corresponding to those of proteins exposed on the surface of L cells. Two of them were cleaved by both trypsin and chymotrypsin, enzymes that decrease the susceptibility of L cells to infection with C. psittaci. These proteins may therefore be involved in the attachment and ingestion of C. psittaci by L cells.

Animals↗

PubMed1981

Attachment defect in mouse fibroblasts (L cells) persistently infected with Chlamydia psittaci.

Almost all the cells in populations of mouse fibroblasts (L cells) persistently infected with the 6BC strain of Chlamydia psittaci were immune to superinfection with high multiplicities of C. psittaci, whether or not the L cells contained visible chlamydial inclusions. As ascertained by experiments with 14C-labeled C. psittaci, immunity to superinfection resulted from the failure of added chlamydiae to attach to persistently infected host cells. However, when exogenous C. psittaci was introduced into persistently infected L cells by centrifuging the inoculum onto host cell monolayers or by pretreating the monolayers with diethylaminoethyl-dextran, these chlamydiae produced expected numbers of infectious progeny. Persistently infected L cells were associated in an unknown way with a C. psittaci population that entered the host cells only with the aid of centrifugation or pretreatment with diethylaminoethyl-dextran. Inclusion-free, persistently infected L cells appeared to present at least two separate hindrances to chlamydial activity: blockage of the attachment of exogenous elementary bodies to persistently infected host cells and prevention of the initiation of chlamydial multiplication by means of a normal developmental cycle in the absence of added C. psittaci.

Animals↗