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J L Yates

Publications and source records attributed to J L Yates.

At least 37 records · Page 2Linked to original sources
PubMed1991

T cell-mediated immunity in the lung: a Cryptococcus neoformans pulmonary infection model using SCID and athymic nude mice.

T cells are important in systemic anticryptococcal defenses, but a role in controlling an initial pulmonary infection has not been demonstrated. A murine model with intratracheal inoculation was developed to study the acquisition and expression of pulmonary T cell-mediated immunity against Cryptococcus neoformans. Infections with four strains of C. neoformans (305, 68A, 613D, and 52D) in two strains of mice (BALB/c and C57BL/6) were examined. Unencapsulated strain 305 and slowly growing strain 68A were readily controlled apparently by nonimmune pulmonary defenses, and no extrapulmonary dissemination was detected. Strain 613D grew progressively in the lungs and disseminated to the brain and spleen. Strain 52D initially grew rapidly in the lungs and disseminated to the spleen, but a clearance mechanism developed in the lungs after day 7 postinfection and in the spleen after day 28. SCID and athymic nude mice were unable to clear a strain 52D pulmonary infection, and a lethal disseminated infection occurred. Pulmonary clearance could be adoptively transferred into SCID mice infected with strain 52D by use of immune T cells from the spleen and lungs and hilar lymph nodes of infected immunocompetent donors. Furthermore, pulmonary clearance was almost 100-fold better in SCID mice that received immune T cells from the lungs and hilar lymph nodes than in those that received immune T cells from the spleen, even though equivalent levels of delayed-type hypersensitivity were transferred by both cell populations. These adoptive transfer studies suggested that the lung and hilar lymph node T cells from immune animals either are enriched in such a way as to mediate protective immunity or home to the lungs better than do splenic T cells.

Animals↗
PubMed1991

Epstein-Barr virus-derived plasmids replicate only once per cell cycle and are not amplified after entry into cells.

Some possible ways in which replication of plasmids containing the Epstein-Barr virus (EBV) plasmid maintenance origin, oriP, might be controlled were investigated. Virtually all plasmid molecules were found to replicate no more than once per cell cycle, whether replication was observed after stable introduction of the plasmids into cells by drug selection or during the first few cell divisions after introducing the DNA into cells. The presence in the cells of excess amounts of EBNA1, the only viral protein needed for oriP function, did not increase the number of oriP-replicated plasmids maintained by cells under selection. In the cell lines studied, EBNA1 and oriP seem to lack the capacity to override the cellular controls that limit DNA replication to one initiation event per DNA molecule per S phase. The multicopy status of EBV-derived, selectable plasmids appears to result from the initial uptake by cells of large numbers of plasmid molecules, the efficient maintenance of these plasmids, and the pressure of genetic selection against plasmid loss. Other unknown controls must be responsible for the amplification of EBV genomes soon after latent infection of cells.

Cell Cycle↗
PubMed1989

Multiple EBNA1-binding sites are required to form an EBNA1-dependent enhancer and to activate a minimal replicative origin within oriP of Epstein-Barr virus.

EBNA1 activates the EBV plasmid maintenance sequence oriP by binding to its two essential regions. One region is a family of 30-base-pair (bp) repeats and is activated by EBNA1 to act as a transcriptional enhancer. The other region contains a 65-bp dyad symmetry and lacks enhancer function. To explore the functional differences between the two regions, we determined oriP activities as functions of the number of 30-bp repeats and compared them with activities determined when tandem copies of the dyad symmetry region were used to replace the 30-bp repeats. Three conclusions have been drawn. (i) Activation of the 30-bp repeats by EBNA1 to enhance transcription or to permit plasmid maintenance is a highly cooperative process involving at least six or seven 30-bp repeats for full activity. (ii) Tandem copies of the dyad symmetry region cooperatively enhance transcription but are less effective than 30-bp repeats providing a similar number of EBNA1-binding sites. (iii) Tandem copies of the dyad symmetry region alone cooperatively activate replication, suggesting that the region contains the actual origin of replication. We also report that while rodent-derived cell lines do not support replication of EBV-derived plasmids they do permit EBNA1-dependent enhancer activity. EBV plasmid replication thus requires the interaction of EBNA1 or oriP with a host factor that is not required for enhancement of transcription.

Antigens, Viral↗
PubMed1981

Escherichia coli ribosomal protein S8 feedback regulates part of spc operon.

In Escherichia coli the genes coding for the 52 ribosomal proteins (r-proteins) are organized into a number of transcription units located at various regions on the bacterial genome. The expression of r-protein genes is balanced so that individual r-protein synthesis rates change coordinately in response to changing environmental conditions, and significant amounts of free r-proteins do not exist in the cellular pool. We have suggested a model for the balanced regulation of r-protein gene expression, namely that r-protein synthesis and ribosome assembly are coupled so that r-proteins not incorporated into ribosomes prevent the further translation of r-protein mRNA by a feedback regulatory mechanism. The model was tested in vitro by examining the effect of purified r-proteins on DNA directed r-protein synthesis, and in vivo by examining the effect of overproduction of certain r-proteins on the synthesis rates of other r-proteins. In vitro experiments have revealed that some r-proteins (L1, L4, L10, S4 and S8) can selectively inhibit the synthesis of r-proteins whose genes are in the same operon as their own, and that this specific feedback regulation occurs at the level of translation rather than at the level of transcription of mRNA. Regulatory roles for L1, S4 and L4 have also been established by in vivo experiments. We have studied further the feedback regulatory properties of S8 in vivo and in vitro, and report here that the protein regulates a part of the spc operon.

Bacterial Proteins↗
PubMed1981

Ultraviolet light and ultraviolet light-activated composite resins.

In a comparison of the UV light--activated composite resins, Estilux was polymerized to a significantly greater depth than the other composite resins. In general, Lee-fill polymerized the least. When comparing the UV light sources, the Lee light and the Duralux light did not significantly differ from each other, but both polymerized the materials tested to a significantly greater depth than the other light sources. Of the two time exposures, 60-second exposure provided a significantly greater depth of polymerization than 20 seconds for each light with each material.

Chemical Phenomena↗
PubMed1981

Identification of ribosomal protein S7 as a repressor of translation within the str operon of E. coli.

A DNA-directed in vitro protein-synthesizing system was used to demonstrate that r protein S7 has the capacity to inhibit the translation of mRNA for the second and third gene products of the str operon (S7 and EF-G) but not for the first gene product (S12). Translation of mRNA of the last gene product in the operon (EF-Tu) is also probably not inhibited by S7. In addition, we localized the target site for S7 repressor action on the polycistronic str mRNA by examining the repressor activity of S7 in vitro using various template DNAs that contain the gene. The target site was found not to include a promoter-proximal portion of the mRNA for S12. To test for regulatory properties of S7 in vivo, we inserted the S7 gene into a plasmid vector containing the ara regulatory elements such that S7 synthesis was placed under ara control. A specific increase in S7 synthesis caused by stimulation in transcription originating from the arabinose promoter decreased the synthetic rate for EF-G but had no effect on S12 or EF-Tu synthesis.

Bacterial Proteins↗
PubMed1981

Feedback regulation of ribosomal protein synthesis in E. coli: localization of the mRNA target sites for repressor action of ribosomal protein L1.

E. coli ribosomal protein L1 is a translational repressor of the synthesis in vitro of both proteins encoded in the L11 operon (L11 and L1). L1 is shown to act at a single target site within the first 160 bases of the bicistronic mRNA, near (or at) the translation initiation site of the L11 cistron. Synthesis of L1 apparently requires translation of the preceding L11 cistron, allowing regulation of the synthesis of both proteins froma single mRNA target site. This observation suggests a sequential translation mechanism that results in the equimolar synthesis rates of the two proteins observed in vivo. It was found that the presence of 23S rRNA, but not 16S rRNA, relieves translational inhibition by L1. L1 presumably recognizes structural features of the mRNA target site that are homologous to the L1-binding site of 23S rRNA. Although previous work indicated that translationally inhibited ribosomal protein mRNA is degraded in vivo, L1 repressor action in the present in vitro system was found not to involve mRNA degradation.

Bacterial Proteins↗
PubMed1980

E. coli ribosomal protein L4 is a feedback regulatory protein.

We studied the synthesis of ribosomal proteins encoded by the S10 operon, an eleven gene operon from the str-spc region of the E. coli chromosome, using a lambda fus3 DNA-directed, in vitro protein synthesizing system. Addition of ribosomal protein L4 (1 microM) to in vitro protein synthesis reactions caused selective inhibition of synthesis of the promoter-proximal proteins of the S10 operon, S10, L3, L4, L23 and possibly L2. Proteins of the S10 operon other than L4 did not cause selective inhibition of protein synthesis. Autoregulatory ribosomal proteins previously identified from other operons, L1, S4 and S8, did not inhibit protein synthesis from the S10 operon; nor did L4 cause significant inhibition of protein synthesis from operons other than the S10 operon. As with L1, S4 and S8, L4 inhibits gene expression at the level of translation.

Bacterial Proteins↗