Mutator genes of baby hamster kidney cells.

Two mutator genes of mammalian cells were demonstrated. One was associated with the ribonucleoside diphosphate reductase, and the other was associated with an extreme adenosine sensitivity.     

Condensed tannin,an antibiotic chemical from Gossypium hirsutum

Antibiotic activity against Heliothis virescens was found in flower buds of Gossypium hirsutum, experimental stock Texas 254. Relatively low antibiotic activity was found in hexane extract, high activity in methanolic extract and residue, and no activity in acetone and water extracts. A condensed tannin having a molecular weight of 4850 was isolated from methanolic extract by column chromatography on Sephadex G-25. It was the major antibiotic component, 3.4% of the dried flower bud. The condensed tannin at 0.2% in the diet retarded larval growth by 84%.     

The chemistry of human transcortin. The effects of pH, urea, salt, and temperature on the binding of cortisol and progesterone.

The interaction of cortisol and progesterone with pure transcortin was investigated. The temperature dependence of cortisol and progesterone binding is a result of the predominantly negative enthalpy of binding which suggests a very good fit between ligand and protein such that the bonds formed are of the van der Waals type. The optimal pH of cortisol (8.0) and progesterone (8.5) binding suggests involvement of cysteine, histidine, and/or tyrosine residues in the binding process. Transcortin is irreversibly denatured at pH 4.0. The effect of sodium chloride on the binding of both steroids is small. At lower sodium chloride concentrations (less than 0.15 m), binding decreases somewhat with decreasing salt concentration. Urea produces a progressive decrease in the association constants of both steroids which is completely reversible up to 2.0 m and 30% reversible at 3.0 m. Scatchard analysis of cortisol binding in the presence of a constant amount of progesterone and vice versa confirms earlier data obtained on plasma that cortisol and progesterone do not bind at two independent sites. It is not possible, however, to decide whether they bind at the same site or at two interdependent (interacting) sites.     

Direct effect of glucose on the preproinsulin mRNA level in isolated pancreatic islets

The effects of glucose on the preproinsulin mRNA level and the rate of (pro)insulin biosynthesis were examined in isolated mouse pancreatic islets. Relative concentrations of preproinsulin mRNA were quantitated by a RNA-dot hybridization procedure. The level of preproinsulin mRNA in islets incubated for up to 7 days at 20 mM glucose remained constant. In islets incubated at 3.3 mM glucose the preproinsulin mRNA level decreased and was after 24 h reduced to one tenth of the level at 20 mM glucose. Subsequent incubation at 20 mM glucose completely restored the preproinsulin mRNA level but only after 3 days of culture, while the insulin release was restored within 24 h. The insulin-biosynthetic activity of the islets was correlated to the variation in the level of the preproinsulin mRNA. These results suggest that glucose does have a direct influence on the level of preproinsulin mRNA and that the rate of (pro)insulin biosynthesis is limited by the level of the preproinsulin mRNA.     

Synthesis and assembly of the synaptic cleft protein S-laminin by cultured cells.

S-laminin, a homologue of the B1 chain of laminin, is concentrated in a subset of basal laminae (BLs), including the BL at the skeletal neuromuscular junction and bears an adhesive site for motoneuron-like cells. Here, we have begun to characterize the native form of the protein. We show that several muscle- and glia-like cell lines synthesize and secrete S-laminin as well as the A, B1, and B2 subunits of the conventional laminin trimer. Experiments using subunit-specific antibodies showed that S-laminin is complexed with the A and B2 subunits of laminin but not with B1, suggesting that S-laminin replaces B1 to form a novel laminin-like trimer. Comparison of material precipitated by different antibodies provided evidence for two immunochemically distinct forms of S-laminin, both of which associate with B2 and A-like subunits. Analysis of tunicamycin-treated cells indicated that N-linked glycosylation is required neither for the selective association of S-laminin with B2 and A subunits nor for the distinction between two forms of S-laminin. Finally, a full-length S-laminin cDNA was constructed and transfected into muscle and non-muscle cells. S-laminin was detected intracellularly in both cell types, in extracellular matrix of muscle cells, and in two immunochemically distinct forms. Thus, the cDNA contains sufficient information to permit assembly, secretion, and post-translational modification of S-laminin.     

Control of experimental autoimmune uveoretinitis by low dose T cell vaccination.

Autoimmune T lymphocytes can be used under appropriate conditions to induce resistance to the specific autoimmune disease that they usually produce. This practice, termed T cell vaccination, was found to be effective with the injection of a low (subpathogenic) number of autoaggressive T line lymphocytes. We report here that T cell vaccination produced marked resistance to the expression of experimental autoimmune uveoretinitis (EAU) in Lewis rats. In addition, vaccination led to the appearance of lymphoid cells in the vaccinated rats that demonstrated proliferative responses against idiotypic and ergotypic specificities of the injected T cells. This is the first report demonstrating the effector T lymphocytes specific for ocular antigens may be used as agents to modulate immunopathogenic responses responsible for EAU.     

Genetics and polymorphism of a duplicated malate dehydrogenase (MDH) locus in the grasshopperOxya japonica japonica (Orthoptera:Acrididae:Oxyinae)

A biochemical genetic study of the enzyme malate dehydrogenase (MDH) was conducted in the grasshopperOxya j. japonica. Analysis of MDH electrophoretic variation in this species of grasshopper shows that one of the two autosomal loci for MDH in grasshoppers, the Mdh-2 locus, controlling the anodal set of MDH isozymes, is duplicated. Results of breeding studies confirm this and the observed polymorphism at theMdh-2 locus in the two populations ofOxya j. japonica studied can be attributed to three forms of linked alleles at the duplicated locus in equilibrium in both populations. In this respect, all individuals of this species possess heterozygous allelic combinations at the duplicatedMdh-2 locus, which may account for the spread of the duplicated locus in the populations of this species of grasshopper.This research was supported by a grant (Vote F) from the University of Malaya, Kuala Lumpur.     

Extrachromosomal human immunodeficiency virus type-1 DNA can initiate a spreading infection of HL-60 cells

In this report, we describe a human immunodeficiency virus type-1 (HIV-1)-infected promyelocytic cell line, OM, derived from HL-60 cells. Although the OM cell line was biologically cloned twice, the pattern of HIV-1 expression during culture appeared analogous to a classical acute spreading infection and was inhibited by both azidothymidine and recombinant soluble CD4 treatment. The number of OM cells actually expressing HIV-1 at the beginning of culture was 0%, reached a peak of nearly 100% at 6 weeks, and then fell to less than 10% HIV-1+ cells by 10 weeks. Clonal analysis of the surviving cells verified that stable HIV-1+ OM cells resulted from the spreading infection. Southern analysis confirmed the transmission of HIV-1 through these OM cultures and the occurrence of stable clones which resulted. The initial percentage of OM cells actually harboring the HIV-1 genome was less than 0.1%, indicating nonfaithful transmission of an unintegrated HIV-1 genome during clonal expansion. These results demonstrate that extrachromosomal HIV-1 DNA can contribute to the spread of HIV-1 infection and give rise to cells which have stably integrated HIV-1 provirus.