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.     

Singlet oxygen induced mutation spectrum in mammalian cells.

In order to characterize the molecular nature of singlet oxygen (1O2) induced mutations in mammalian cells, a SV40-based shuttle vector (pi SVPC13) was treated with singlet oxygen arising from the thermal decomposition of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). After the passage of damaged plasmid through monkey COS7 cells, the vector was shuffled into E. coli cells, allowing the screening of supF mutants. The mutation spectrum analysis shows that single and multiple base substitutions arose in 82.5% of the mutants, the others being rearrangements. The distribution of mutations within the supF gene is not random and some hotspots are evident. Most of the point mutations (98.4%) involve G:C base pairs and G:C to T:A transversion was the most frequent mutation (50.8%), followed by G:C to C:G transversion (32.8%). These results indicate that mutagenesis in mammalian cells, mediated by 1O2-induced DNA damage, is targeted selectively at guanine residues.     

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.     

Sequence preferences of DNA interstrand crosslinking agents: quantitation of interstrand crosslink locations in DNA duplex fragments containing multiple crosslinkable sites.

A general approach to the quantitative study of the sequence specificity of DNA interstrand crosslinking agents in synthetic duplex DNA fragments is described. In the first step, a DNA fragment previously treated with an interstrand crosslinking agent is subjected to denaturing PAGE. Not only does this distinguish crosslinked from native or monoadducted DNA, it is shown herein that isomeric crosslinked DNAs differing in position of the crosslink can in some cases be separated. In the second stage, the now fractionated crosslinked DNAs isolated from denaturing PAGE are subjected to fragmentation using iron(II)/EDTA. For those fractions which are structurally homogeneous, analysis of the resulting fragment distribution has previously been shown to reveal the crosslink position at nucleotide resolution. It is shown herein that in fractions which are structurally heterogeneous due to differences in position of crosslink, this analysis quantifies the relative extent of crosslinking at distinct sites. Using this method it is shown that reductively activated mitomycin C crosslinks the duplex sequences 5'-GCGC and 5'-TCGA with 3 +/- 1:1 relative efficiency.     

Photoaffinity labeling of scorpion toxin receptors associated with insect synaptosomal Na+ channels

Photoreactive and radioiodinated derivatives of several scorpion toxins acting on insect Na+ channels were prepared without loss of their pharmacological activities. Photoaffinity experiments were carried out on a synaptosomal fraction from the nerve cord of the cockroach Periplaneta americana: with all toxin derivatives, a single specifically labeled band was obtained with a molecular weight of 188,000 +/- 12,000 (n = 17). These results indicate for the first time the molecular weight of the scorpion toxin receptor from the insect nervous system which is probably associated with voltage sensitive Na+ channels. One of these toxins, toxin VII from Tityus serrulatus venom, has been previously shown to be active both in mammals and in insects, in rat brain synaptosomes this toxin labeled a Mr = 31,000 +/- 4,000 band in contrast, to observations in the insect preparation.