Primary and secondary structures of Tetrahymena and aphid 5.8S rRNAs: structural features of 5.8S rRNA which interacts with the 28S rRNA containing the hidden break

The Tetrahymena 5.8S rRNA is 154 nucleotides long, the shortest so far reported except for the split 5.8S rRNAs of Diptera (m5.8S plus 2S rRNA). In this molecule several nucleotides are deleted in the helix e (GC-rich stem) region. Upon constructing the secondary structure in accordance with "burp-gun" model, the Tetrahymena 5.8S rRNA forms a wide-open "muzzle" of the terminal regions due to both extra nucleotides and several unpaired bases. The aphid 5.8S rRNA consists of 161 nucleotides and can form stable helices in both terminal and helix e regions. As a whole, the secondary structure of Tetrahymena 5.8S rRNA resembles that of Bombyx 5.8S molecule while the aphid 5.8S rRNA shares several structural features with the HeLa 5.8S molecule. Likely, the 5.8S rRNA attached to the 28S rRNA with the hidden break differs in structure from those interacting with the 28S partners without the break. Nucleotide sequences of 5.8S rRNA in insects as well as in protozoans are not so conservative evolutionarily as in vertebrates.     

H2Kk can influence whether cytotoxic T lymphocytes recognize trinitrophenyl in association with H2Dk unique or H-2Kk and H-2Dk shared self determinants

The present study investigates the effect of trinitrophenyl- (TNP) modified H-2Kk (TNP-Kk) antigens on the generation of anti-TNP-Dk restricted cytotoxic T lymphocyte (CTL) responses. C3H.OH mice were primed to TNP-self by skin-painting with trinitrochlorobenzene, and spleen cells from these primed mice were subsequently stimulated in vitro with TNP-self. The effector cells generated exhibited appreciable lysis of TNP-modified C3H.OH blast target cells. Cold target inhibition studies demonstrated the generation of two effector cell populations: one that recognizes TNP in association with unique Dk self determinants, and one that recognizes TNP in association with self determinants shared between TNP-Kk and TNP-Dk. This was in contrast to primed C3H/He spleen cells, which did not generate CTL that recognized TNP in association with unique Dk self determinants. When spleen cells from (C3H/He x C3H.OH)F1 mice primed to TNP were stimulated in vitro with TNP-C3H.OH cells, unique Dk self determinants were recognized in association with TNP. However, in vitro stimulation of the same F1 responding cells with TNP-C3H/He or TNP-F1 cells failed to elicit CTL that utilized these Dk-unique self determinants. The findings of this study demonstrate that unique or shared H-2Dk determinants can be differentially utilized by CTL populations, depending on the H-2 alleles expressed by the stimulator cells.     

Antipain and 12-O-tetradecanoyl-phorbol-13-acetate: Phenomenology of effects on UV mutagenesis in V79 Chinese hamster cells

Antipain (AP) and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were tested in V79 Chinese hamster cells for cytotoxicity and effects on survival and 6-thioguanine-resistant (6TG^r) mutation after UV-irradiation. AP and/or TPA were relatively non-cytotoxic and had no significant effects on UV survival. Despite their non-mutagenicity, the recovery of UV-induced 6TG^r colonies was significantly enhanced by the pretreatment with either AP (0.5–2 mM) or TPA (0.1–1 μg/ml) only during the expression period before the 6TG selection at a low density of cells in the absence of AP or TPA. Such enhancing effects were maximal when AP or TPA was present during the late expression period after the mutation fixation and extensive dilution of DNA lesions. Reconstruction experiments revealed the antagonistic actions that TPA and AP tended to eliminate and increase, respectively, the metabolic co-operation. In the TPA-plus-AP treatment, AP abolished the TPA-enhanced recovery of induced mutants. Thus, it seems that TPA increases the mutant recovery largely through decreased metabolic co-operation and AP could modulate the mutation expression. Further, an error-prone inducible repair may not exist or, if it exists, AP may not inhibit it in V79 Chinese hamster cells.     

Hydrocephalus in suckling rats infected intracerebrally with mouse hepatitis virus, MHV-A59

After intracerebral inoculation of mouse hepatitis virus, MHV-A59 strain, into 3- to 5-day-old Wistar rats, some survivors at 14 days postinoculation (p.i.) were found to lack the cerebral cortex and to have an accumulation of considerable amount of cerebrospinal fluid. The virus titer in the brain increased exponentially after inoculation, reaching a maximum 4 to 6 days p.i. when immunofluorescence revealed virus-specific antigen within neurons in the cerebral cortex. A small amount of infectious virus was also detectable 14 days p.i. when the cerebral anomaly was evident. This brain malformation causing hydrocephalus was due to cerebral damage by viral infection.     

The induction in vitro of immunological tolerance in T lymphocytes: an inhibitory role of macrophages.

Hapten-reactive helper T cells were generated in the spleen of C57BL/6 mice primed with sulfanilated syngeneic IgG (S-MGG). Specific immunological tolerance was induced in vitro in these helper T cells, when spleen cell suspension was passed through Sephadex G-10 column to remove adherent cells and cultured in the presence of soluble S-MGG for 21 to 24 hours. On the other hand, tolerance was not inducible in unfractionated, primed spleen cells. When G-10-passed spleen cells were added to the culture dishes containing phagocytic, adherent cells of the spleen, tolerance was no more inducible in these reconstituted cell population. From these experimental results, it was concluded that macrophages played an interfering role in tolerance induction. The experimental data were also discussed in terms of macrophage function in the recognition of antigen by T lymphocytes.     

Replicative bypass repair of ultraviolet damage to DNA of mammalian cells: Caffeine sensitive and caffeine resistant mechanisms

Replicative bypass repair of UV damage to DNA was studied in wide variety of human, mouse and hamster cells in culture. Survival curve analysis revealed that in established cell lines (mouse L, Chinese hamster V79, HeLa S3 and SV40-transformed xeroderma pigmentosum (XP)), post-UV caffeine treatment potentiated cell killing by reducing the extrapolation number and mean lethal UV fluence (Do). In the Do reduction as the result of random inactivation by caffeine of sensitive repair there were marked clonal differences among such cell lines, V79 being most sensitive to caffeine potentiation. However, other diploid cell lines (normal human, excision-defective XP and Syrian hamster) exhibited no obvious reduction in Do by caffeine. In parallel, alkaline sucrose sedimentation results showed that the conversion of initially smaller segments of DNA synthetized after irradiation with 10 J/m² to high-molecular-weight DNA was inhibited by caffeine in transformed XP cells, but not in the diploid human cell lines. Exceptionall, diploid XP variants had a retarded ability of bypass repair which was drastically prevented by caffeine, so that caffeine enhanced the lethal effect of UV. Neutral CsCl study on the bypass repair mechanism by use of bromodeoxyuridine for DNA synthesis on damaged template suggests that the pyrimidine dimer acts as a block to replication and subsequently it is circumvented presumably by a new process involving replicative bypassing following strand displacement, rather than by gap-filling de novo. This mechanism worked similarly in normal and XP cells, whether or not caffeine was present, indicating that excision of dimer is not always necessary. However, replicative became defective in XP variant and transformed XP cells when caffeine was present. It appears, therefore, that the replicative bypass repair process is either caffeine resistant or sensitive, depending on the cell type used, but not necessarily on the excision repair capability.     

Stable phylloplane colonization by entomopathogenic bacterium Pseudomonas fluorescens KPM-018P and biological control of Phytophagous ladybird beetles Epilachna vigintioctopunctata (Coleoptera: Coccinellidae)

An entomopathogenic bacterium was isolated from tomato leaves and used as a microbial agent to control larvae of phytophagous ladybird beetles Epilachna vigintioctopunctata. The isolate was identified as Pseudomonas fluorescens KPM-018P on the basis of its bacteriological characteristics. KPM-018P produced extracellular chitinase to form a transparent zone around their colonies by hydrolyzing chitin in a minimal medium. Pale-yellow colonies turned red after a change of incubation temperature. These characteristics were availed as markers for tracking KPM-018P. The bacteria produced biosurfactants that enabled the bacteria to stably colonize the hydrophobic leaf surface; they were recovered without any considerable decrease even after a suspension of KPM-018P was sprayed onto leaves. KPM-018P, transformed with the gfp gene and observed with fluorescence microscopy, stably dwelled in the junctions of epidermal cells of bacteria-sprayed leaves. Ingestion of KPM-018P-sprayed leaves by the larvae caused prompt death of these insects to eventually suppress their pupation. This method is thus effective for decreasing the population of larvae and adult insect pests in the subsequent generation. The study provides an experimental basis for the biocontrol of herbivorous insect pests using a leaf-inhabiting, entomopathogenic strain of P. fluorescens.     

The Aspergillus nidulans genes chsA and chsD encode chitin synthases which have redundant functions in conidia formation

 We previously isolated three chitin synthase genes (chsA, chsB, and chsC) from Aspergillus nidulans. In the present work, we describe the isolation and characterization of another chitin synthase gene, named chsD, from A. nidulans. Its deduced amino acid sequence shows 56.7% and 55.9% amino acid identity, respectively, with Cal1 of Saccharomyces cerevisiae and Chs3 of Candida albicans. Disruption of chsD caused no defect in cell growth or morphology during the asexual cycle and caused no decrease in chitin content in hyphae. However, double disruption of chsA and chsD caused a remarkable decrease in the efficiency of conidia formation, while double disruption of chsC and chsD caused no defect. Thus it appears that chsA and chsD serve redundant functions in conidia formation.