Myxococcus xanthus synthesizes a stabilized messenger RNA during fruiting body formation

Initial characterization of the unstable 5S-to-16S RNA fraction from developingMyxococcus xanthus cells reveals that it is rapidly labeled with radioactive RNA precursor and is associated with polyribosomes and released by puromycin from polyribosomes. The total unstable RNA fraction from 10-min pulse-labeled developing cells has a half-life of 13 min, compared with a 4-min half-life for unstable RNA (presumptive mRNA) from vegetative cells pulse-labeled for 2 min. We conclude that this developmental 5S-to-16S RNA contains messenger RNA and that this mRNA is stabilized compared with that in vegetative cells.     

Lymphocytes express Ia antigens of foreign haplotype following treatment with neuraminidase

Evidence is presented which indicates that neuraminidase (NA) treatment of spleen cells both destroys old Ia antigens and reveals new Ia specificities which are not normally expressed by splenocytes. It was found that NA treatment unmasked alien I-A^k-like specificities on A.TH (I ^s ) spleen cells, and I^s-like antigens on A.TL (I ^k ) spleen cells. These conclusions were based on direct testing of NA-treated targets with a range of alloantisera and on cell-absorption experiments. Furthermore, the cellular distribution of NA-exposed antigens resembled that of convential Ia antigens, the new antigens being expressed on more than 90 percent of splenic B cells and a subpopulation of splenic T cells. However, although some of the antigens exposed by NA on A.TH cells appeared to resemble the Ia. 3 and 15 specificities, additional antigens were involved which did not correlate with any previously described Ia antigens.Sugar inhibition experiments demonstrated the NA-exposed antigens to be carbohydrate in nature, D-galactose being an effective inhibitor in these studies. The proportion of- and-linked D-galactose residues associated with the new antigens depended upon the target cell used and the anti-Ia serum tested. Furthermore, glycolipid extracts from lymphoid cells were shown to contain the NA-exposed antigens.Collectively, these results support the existence of carbohydrate-defined Ia antigens. The simplest interpretation of the findings is that NA clips off terminal sialic acid residues from carbohydrate-defined Ia antigens on the cell surface and exposes subterminal sugars which resemble antigens expressed by otherI-region haplotypes.     

Molecular mechanisms of temperature adaptation in fish myofibrillar adenosine triphosphatases

Summary Studies have been carried out on the Mg²⁺ Ca²⁺-myofibrillar ATPase from the muscles of fish adapted to different environmental temperatures. The thermal stability of the ATPase is strongly correlated with mean habitat temperature. Activities of Antarctic fish ATPases are significantly higher at low temperatures than those of temperate and tropical water species. The effects of ionic strength on ATPase activity have also been studied. The Gibbs free energy of activation (G ^#) was found to increase and enzyme activity decrease with increasing ionic strength within the physiological temperature range of each species. Significantly lower values of G ^#, of around 1 Kcal/mole, are obtained for the ATPase of cold-adapted compared to tropical fish. Enthalpic and entropic activation energies were also reduced in the cold adapted ATPases. It is postulated that the reduction of the enthalpic activation term in the cold adapted enzyme confers the advantage of reducing the temperature sensitivity of the rate limiting step thus partly compensating for the low heat content of the cellular environment. Possible molecular mechanisms of temperature compensation in fish myofibrillar ATPase are discussed.     

Identifying sites of simultaneous DNA replication in eukaryotes by N-methyl-N''-nitro-N-nitrosoguanidine multiple mutagenesis.

Summary N-methyl-N-nitro-N-nitrosoguanidine (NG) induces certain classes of multiple mutations in yeast at high frequency. By selecting for mutation at one locus (his4 or leu1) one frequently obtains double mutants where another mutation to temperature sensitivity has also been induced. This multiple mutagenesis exhibits a considerable specificity: for mutation at one particular locus there is a high chance that another mutation will be found in the same cell at one of a restricted number of other loci. For any given locus (e.g. his4) there is a spectrum of sites at which temperature-sensitivity mutations are coinduced. This spectrum differs for different loci, such that the spectrum of sites co-mutating with leul differs completely from that for sites co-mutating with his4. This NG-induced co-mutation is interpreted in terms of NG acting to enhance mutagenesis at sites of simultaneous DNA replication within the cell. The results so obtained indicate a very strict control over the order and timing of gene replication in Saccharomyces cerevisiae, and it is suggested that it is now possible to use NG double mutagenesis to try and locate origins of replication in yeast.     

Variabilin,a 6a-hydroxypterocarpan from Dalbergia variabilis

Bark and wood of the creeper Dalbergia variabilis contain the previously described friedelin, O-acetyl-oleanolic acid, formononetin, 8-O-methylretusin, (+)-vestitol, (±)-mucronulatol, (+)- and (±)-medicarpin, besides (+)-variabilin [(6aR,11aR)-6a-hydroxy-3,9-dimethoxypterocarpan]. This structure was confirmed by the conversion of (+)-variabilin into di-O-methylcoumestrol.     

Effects of Monovalent and Divalent Cations on 3-(+)[125I]Iododizocilpine Binding to the N-Methyl-d-Aspartate Receptor of Rat Brain Membranes

We have investigated the binding of 3-[125I]iododizocilpine ([125I]iodo-MK-801) to the N-methyl-D-aspartate (NMDA) receptor in well-washed rat brain membranes. [125I]Iododizocipline binding was displaced by the following: dizocilpine greater than thienylphencyclidine greater than phencyclidine greater than ketamine. Binding of [125I]iododizocilpine was enhanced by glutamate, glycine, and spermidine, whose actions could be reversed by CGS-19755, 7-chlorokynurenate, and arcaine, respectively. [125I]Iododizocilpine binding was also enhanced by a number of divalent cations, including Ba2+, Ca2+, Mg2+, Mn2+, and Sr2+, and several monovalent cations, including Na+ and K+. These cations enhanced [125I]iododizocilpine binding by an action at the polyamine site. In addition, the inhibitory effects associated with high concentrations of these cations was markedly reduced compared to those found in previous studies with [3H]dizocilpine. Analysis of the ability of spermidine, Mg2+, and Sr2+ to alter the inhibition of [125I]iododizocilpine by arcaine gave pA2 values of 5.41, 4.47, and 4.93, corresponding to EC50 concentrations of 3.9, 34.7, and 12.0 microM, respectively, suggesting that physiological concentrations of Mg2+ may occupy the polyamine site. These results demonstrate that [125I]iododizocilpine is a useful probe for the NMDA receptor. Moreover, its high specific activity and relative insensitivity to the inhibitory actions of divalent cations should make [125I]iododizocilpine a valuable ligand for the study of NMDA receptors in intact cellular systems.     

Proteolytic degradation of heterologous proteins expressed inAspergillus niger

Summary Proteolytic degradation of heterologous proteins expressed in the filamentous fungusAspergillus niger reduces the yield of authentic target protein. The activities ofA. niger proteases are differentiated by their effects on two proteins expressed and secreted fromA. niger: hen egg-white lysozyme and porcine pancreatic phospholipase A₂.     

Empruthotrema dasyatidis n. sp. (Monogenea: Monocotylidae) from the olfactory sacs of Dasyatis fluviorum (Rajiformes: Dasyatidae) from Moreton Bay,Queensland

The monocotylid monogenean Empruthotrema dasyatidis n. sp. is reported from the olfactory sacs of the brown stingray, Dasyatis fluviorum Ogilby, 1908, from Moreton Bay, Queensland, Australia. This is the first record of Empruthotrema from the family Dasyatidae. E. dasyatidis n. sp. differs from other species of Empruthotrema by possessing eye pigment, which may be scattered, and by its small size. The generic diagnosis for Empruthotrema is amended.