Effects of oxygen and sulphydryl-containing compounds on irradiated transforming DNA. III. Reaction rates

The absolute rate for the repair reaction of radiation-induced, oxygen-dependent lesions in bacterial transforming DNA with the sulphydryl (SH)-containing compound dithiothreitol (DTT) has been determined using a fast response method, the gas explosion technique, to be 1.6 X 10(6) mol-1 s-1. Glutathione reacts ten times slower than DTT with the irradiated transforming DNA. It can also be calculated that transforming DNA radicals react with O2 in a damage-fixing reaction with a rate of about 3 X 10(8) dm3 mol-1 s-1. These rates are compared with values in the literature for reaction rates of SH, compounds and O2 with irradiated DNA constituents and with bacterial cells.     

Identification of a tumor inhibitory factor in rat ascites fluid

A polypeptide which inhibits the growth of human carcinoma cells has been characterized from Novikoff rat ascites fluid. This tumor inhibitory factor co-purified with transforming growth factor activity through acid/ethanol extraction and Bio-Gel chromatography. The two activities were completely separated by reverse phase HPLC. The tumor inhibitory factor is heat stable and requires disulfide bonds for bioactivity. This factor inhibited the anchorage independent growth of the more differentiated human colon carcinoma cell lines but did not affect the less differentiated carcinoma cells. The presence of stimulatory and inhibitory activities in the same extracts suggests that the relative concentrations of these factors may be important in the control of cell growth.     

Kinetic Effects of Terbium Ions on Muscarinic Acetylcholine Receptors of Murine Neuroblastoma Cells

Preincubation of murine neuroblastoma cells (clone N1E-115) with terbium chloride resulted in a significant potentiation of carbachol-mediated increase in cyclic GMP formation. This effect was accompanied by a shift of the peak response from 30 s to 120 s and a 6-fold decrease in carbachol concentration producing half-maximal responses, in addition to a significant increase in the Hill coefficient. Terbium ions also caused a significant decrease in the affinity and an increase in the maximum binding of [3H]quinuclidinyl benzilate to muscarinic receptors, the change in affinity being mainly due to a decrease in the association rate. Preincubation of cells with 1 mM carbachol for 4 h (the desensitized state of the muscarinic receptor) resulted in a decrease in the ability of terbium to alter [3H]quinuclidinyl benzilate binding. The effects of terbium reported here might be due to its affecting muscarinic receptor-effector coupling, which is considered to be lost upon receptor desensitization.     

Decreased High-Affinity Binding of [3H]Muscimol to Cerebral Synaptic Membranes of Scrapie-Infected Mice

Scrapie is a transmissible disease that results in progressive degeneration of the central nervous system and death. Although scrapie has been studied histopathologically, relatively little is known concerning neurotransmitter alterations. Specific [3H]muscimol binding to whole brain crude synaptic membranes (CSM) from mice clinically affected with scrapie was significantly (p less than 0.01) reduced, to approximately 73% of that of the controls. Of the brain regions examined, binding to only cerebral CSM was significantly (p less than 0.0001) decreased. Scatchard analyses of saturation curves revealed that the high-affinity (KD = 8 +/- 3 nM) site for muscimol was abolished in cerebral CSM from scrapie-infected mice, while the low-affinity site was unaffected. Binding of [3H]flunitrazepam to cerebral CSM was unaffected by scrapie and was stimulated by GABA to the same extent in both scrapie and control mice. These results suggest that scrapie agent 139A in C57BL/6J mice manifests a portion of its CNS pathology via a high-affinity GABA binding site that is unassociated with the benzodiazepine receptor.     

Turbo Tree: a fast algorithm for minimal trees

A branch and bound algorithm is described for searching rapidlyfor minimal length trees from biological data. The algorithmadds characters one at a time, rather than adding taxa, as inprevious branch and bound methods. The algorithm has been programmedand is available from the authors. A worked example is givenwith 33 characters and 15 taxa. About 8 x 10¹² binary treesare possible with 15 taxa but the branch and bound program findsthe minimal tree in <5 min on an IBM PC. Received on January 15, 1987; accepted on February 23, 1987     

HLA-JY328: Mapping studies and expression of a polymorphic HLA class I gene

The JY328 clone was identified in a human genomic library using cDNA corresponding to mRNA for HLA-B7 as a probe. The L/328 cell line was established by cotransformation of mouse Ltk^– cells with the herpes thymidine kinase gene and clone JY328. On Northern blots, RNA from,L/328 strongly hybridized to an HLA class I probe, and an antigen was recognized by an anti-HLA class I framework antibody on the cell surface. A DNA probe corresponding to a segment of intron 7 was developed by comparing the nucleotide sequence of clone JY328 with that of other HLA class I-type genes. Using the radiolabeled probe to screen Southern blots of DNA from families with siblings exhibiting intra-HLA recombinations, a restriction fragment length polymorphism was revealed —a 1.4 kb BstE II band not present in all individuals. A corresponding fragment was apparent in the base sequence of clone JY328. The occurrence of this band on Southern blots established that JY328 maps distinct from and centromeric to the HLA-C locus and near to the HLA-B locus. Antibody absorption studies and cytotoxicity tests indicated that the JY328 gene product was not an HLA-B antigen but that it did specifically absorb CW7-specific antibody. In sum, these results suggest a novel, polymorphic HLA class I gene which expresses a product serologically similar to HLA-Cw7 but which does not map within the corresponding locus.     

The stimulation of anthraquinone production by Cinchona ledgeriana cultures with polymeric adsorbents

Summary Anthraquinones produced by suspension cultures of Cinchona ledgeriana are released into the medium, which becomes saturated with products late in the growth cycle. When a high affinity polymeric adsorbent, such as the macro-reticular Amberlite XAD-7, is added to the culture the concentration of anthraquinone in the medium is maintained at a low level and production may be stimulated 15-fold, yielding up to 20 mg/1/day. More than 90% of the product is released from the cells. For maximal yields it is shown that both the amount of adsorbent used and the time after sub-culture at which it is added to the system are critical. The value of such a method for product recovery from immobilised cells is discussed.     

Paleolimnology of the Peten Lake District,Guatemala

Long-term changes of sedimentary particle-size distribution in two tropical lowland lakes were compared with changes of human population sizes, estimated archaeologically, in the drainage basins. Mean particle size of silt and clay fractions (<64 µm) varied between 3 and 15 µm. High positive skewness and kurtosis of the distributions were associated with smaller particle sizes; hence small mean size resulted from greater influx of small particles while influx of larger particles was probably constant. An inverse correlation between mean particle size and human population size is interpreted to mean that disturbance-induced erosion results in delivery of very fine inorganic particles at higher rates. Within any one basin, particle-size stratigraphy is more precisely related to archaeological time periods than is pollen stratigraphy. An absolute chronology still eludes us, owing to the failure of ¹⁴C dating of calcareous, colluvial sediments, but our relative chronology is now more precise than before. If certain assumptions about past hydrologic relations can be met, particle-size analysis is a way of comparing the histories of geographically very different lakes, including lakes from tropical, temperate, and arctic regions.     

From synthetic antigens to synthetic vaccines

The availability of synthetic antigens permitted a systematic elucidation of the molecular basis of antigenicity, as well as of other phenomena, and to establish the genetic control of immune response and its link to the major histocompatibility region of the species. Moreover, it allowed a conceptual approach to production of vaccines made up of synthetic fragments of relevant virus antigens. This was first demonstrated with a bacteriophage, MS-2, that can be efficiently inactivated with antibodies obtained with an immunogen in which a synthetic peptide corresponding to a sequence of 20 amino acid residues within its coat protein was covalently linked to a polymeric synthetic carrier. When the synthetic adjuvant N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) was chemically linked to the same molecule, the resulting immunogen was effective in aqueous solution. This approach has now been used for diphtheria: a synthetic peptide from the A-chain of the toxin, covalently attached together with MDP to the synthetic carrier multichain poly(DL-alanine) induced antibodies cross-reactive with the diphtheria toxin as well as protection against the dermonecrotic activity of the toxin. A similar approach has been described also by R. Arnon and her colleagues in our laboratory for influenza virus, making use of a peptide with sequence 91–108 of the hemagglutinin of type A H₃N₂ strains attached to tetanus toxoid. The results indicated that the conjugate led to partial protection against A/Texas mouse-adapted influenza virus.