A novel class of ammonium assimilation mutants of the photosynthetic bacterium Rhodobacter capsulatus

Nitrogen assimilation in Rhodobacter capsulatus has been shown to proceed via the coupled action of glutamine synthetase (GS) and glutamate synthase (GOGAT) with no measurable glutamate dehydrogenase (GDH) present. We have recently isolated a novel class of mutants of R. capsulatus strain B100 that lacks a detectable GOGAT activity but is able to grow at wild type rates under nitrogen-fixing conditions. While NH ₄ ⁺ -supported growth in the mutants was normal under anaerobic/photosynthetic conditions, the growth rate was decreased under aerobic conditions. Ammonium and methylammonium uptake experiments indicated that there was a clear difference in the ammonium assimilatory capabilities in these mutants under aerobic versus anaerobic growth. Regulation of expression of a nifH : : lacZ fusion in these mutants was not impaired. The possible existence of alternative ammonium assimilatory pathways is discussed.     

Social stimuli fail to act as entraining agents of circadian rhythms in the golden hamster

Summary The ability of social stimuli to act as entraining agents of circadian rhythms was investigated in golden hamsters (Mesocricetus auratus). In a first experiment, pairs of male hamsters (one of them enucleated and the other intact) were maintained under a light-dark (LD) cycle with a period of 23.3 h. Running-wheel activity was recorded to determine the effect of social interaction on the free-running circadian rhythm of activity. In several pairs, general activity and body temperature were also recorded. In all pairs the intact animals entrained to the LD cycle, whereas the activity rhythms of the enucleated animals free-ran with periods of approximately 24 h and showed no apparent sign of synchronization or relative coordination with the other member of the pair. In a second experiment, male hamsters maintained in constant darkness received pulses of social interaction, which have been reported to induce phase shifts of the activity rhythm. Consistent phase shifts in the running-wheel activity rhythm were not induced by the social pulses in our experiment. These results suggest strongly that social stimuli are not effective entraining agents of circadian rhythms in the golden hamster.Abbreviations CT circadian time - LD light-dark     

A nomenclature for the genes encoding the chlorophylla/b-binding proteins of higher plants

We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present a table for the conversion of old gene names to the new nomenclature.     

Ethylene and in vitro rooting of hazelnut (Corylus avellana) cotyledons

Ethylene may be one of the many factors that play a role in rooting. However, in some studies ethylene promoted rooting, while in others it was inhibitory or had no effect. Using cotyledons of hazelnut ( Corylus avellana L. cv. Casina) observations were made of the effect of ethylene precursors on adventitious root formation. l-methionine (Met) or 1-aminocyclopropane-1-carboxylic acid (ACC) added to a standard indole-3-butyric acid (IBA)-kinetin-containing medium did not enhance rooting, while 2-chloroethylphosphonic acid (CEPA) did. The ethylene inhibitor, aminoethoxyvinylglycine (AVG), inhibited root formation, but its effect was reversed by ACC when cotyledonary segments were transferred to rhizogenic medium plus ACC at day 10. Ethylene production by cotyledons cultured on rhizogenic medium or rhizogenic medium plus CEPA was high at the beginning of rooting. Thus, the wound-induced ethylene is a key stimulatory factor in the formation of root primordia. The data support the hypothesis that ethylene plays a positive role in root formation.     

Detection of complex alleles by direct analysis of DNA heteroduplexes

DNA molecules derived from three alleles of the HLA-DRB3 locus and differing from each other at several nucleotide sites were denatured and cross-hybridized. Each allelic combination was found to generate a pair of heteroduplexes of different mobility. Their retardation as compared to homoduplexes was proportional to the number of mismatches. In each heteroduplexes pair the component possessing the highest number of Pyr-Pyr oppositions was the most retarded. The results are those predicted by a theoretical model implying a correlation between base-pair opening and bending of the DNA double helix. These observations introduce a new HLA typing method at the genomic level and indicate an experimental approach to the analysis of the superhelical DNA conformation as related to different types of base oppositions.     

1H- and13C-NMR spectroscopic studies of lipid extracts of the red algaGracilaria longa

Lipid extracts of the red algaGracilaria longa were studied by¹H- and¹³C-NMR spectroscopy. Peaks in the¹³C-NMR spectra attributable to sterols, chlorophylls and carotenoids allowed free and acylated cholesterol, chlorophylla and lutein to be identified as the most abundant components of these classes. A content of 0.5 ± 0.1 μmoles of total cholesterol/g wet alga was estimated from the¹H-NMR spectrum, which also allowed the determination of the phosphatidylcholine/total lipid molar ratio (9.5 ± 0.5%). The¹³C-NMR spectroscopic experiments provided information on the position of the double bonds on the fatty acid residues. A comparison between NMR spectra of lipid extracts obtained for wet and dried alga showed that the alga undergoes both a dramatic peroxidation and some glycolipid degradation during the drying process.     

Computer-assisted mathematical analysis of sigmoid biological events

A program in BASIC is described which allows accurate quantificationof some numerical parameters that can be objectively correlatedto biological indexes in sigmoid biological events. Attentionwas focused on the polymerization process of actin (a muscleprotein with a mol. wt of 42 000 daltons) studied as the variationin the OD₃₆₀ index with time. The experimental points, if plotted,can be well approximated by a rational function of the typeOD₃₆₀ = f(t), which passes through the origin and can be representedgraphically by a sigmoid curve. The program was very helpfulin comparing the experimental curves and in analysing significantparameters, such as maximum velocity and asymptote, that characterizethese curves and whose interpretation would otherwise be purelysubjective. Received on July 11, 1985; accepted on January 13, 1986     

Effect of Eimeria falciformis infection on the development of toxoplasmosis in mice

White mice previously infected with 10(2), 10(3) or 10(4) Eimeria falciformis oocysts on days 0, 5, 10 or 30 were inoculated per os with 10(1), 10(2), 10(3) or 10(4) Toxoplasma oocysts. While the results obtained for mice with higher Toxoplasma inocula were consistent, animals with 10(1) and 10(2) oocysts previous inoculation with Eimeria showed important differences related with those infected only with Toxoplasma. For example, survival time was higher in animals infected with both parasites, especially if inoculated with Eimeria 30 days before Toxoplasma infection. Furthermore the number of T. gondii cysts found in the animals previously infected with Eimeria was lower compared with mice inoculated with Toxoplasma only. Body weight of mice infected with Toxoplasma previous infection with Eimeria was almost normal in relation to those infected only with Toxoplasma, indicating a probable pathological effect due to the parasite, more evident in "non immunized" mice.     

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.