The dark-colour-inducing neurohormone of locusts in relation to an albino mutant of Schistocerca gregaria

In the albino mutant of an Okinawa strain of Locusta migratoria (L.) (Orthoptera: Acrididae), albinism is caused by the absence of the dark‐colour‐inducing neurohormone (DCIN), which is present in the corpora cardiaca (CC) of normally coloured phenotypes. This study tests whether the absence of DCIN is responsible for albinism in an albino mutant of another locust, Schistocerca gregaria (Forsk.) (Orthoptera: Acrididae). This seemed feasible because a single Mendelian unit controls albinism in both species. However, implantation of CC, or injection of an extract of CC, from albino donors of S. gregaria, induce dark coloration in crowded nymph recipients of the Okinawa albino mutant of L. migratoria, as effectively as do implanted CC, or injections of extract of CC, from normal phenotype donors of S. gregaria. Therefore, DCIN is present in the albino mutant of S. gregaria, and consequently, the albinism in this mutant is not caused by its absence. Implantation of CC, or injection of extracts of CC, from albino donors of S. gregaria to conspecific albino nymphs does not induce darkening. Only extremely high doses of synthetic DCIN injected into albino nymphs of S. gregaria are effective, inducing some darkening. The dose to induce such darkening in albino nymphs of S. gregaria is 50 nmol, ≈ 5 × 10⁶ times higher than that (10 femtomol) needed to induce equivalent darkening in nymphs of the Okinawa albinos of L. migratoria. The results are discussed and some possible explanations of the observed effects outlined.     

Autonomous replication sequences in an extrachromosomal element of a pathogenic Entamoeba histolytica.

Entamoeba histolytica possesses a 24.5 kilobase plasmid-like molecule which encodes for the organism's ribosomal RNAs. Sequence analysis of this extrachromosomal element revealed the presence of AT rich sequences which show homology to the origin of replication of other lower eucaryotes. An 802 bp fragment containing these sequences was cloned into a yeast shuttle vector lacking the origin of replication and the construct tested for its ability to replicate autonomously in yeast. Mitotic stability tests as well as evidence for plasmid maintenance indicate that the transformed cells contained self-replicating episomes and not stably integrated molecules. The nucleotide sequence of this ARS-containing fragment is presented.     

Conopy architecture of Larrea tridentata (DC.) Cov., a desert shrub: foliage orientation and direct beam radiation interception

Summary At sites in the United States, creosote bushes (Larrea tridentata (DC.) Cov.) orient foliage clusters predominantly toward the southeast. Foliage of bushes at the southernmost distribution extreme in Mexico shows no predominant orientation. Clusters at all sites are inclined between 33° and 71° from the horizontal. Inclinations are steeper in the drier and hotter Mojave Desert than in the Chihuahuan Desert. Individual leaflets, though not measured, appear more randomly oriented than foliage clusters. In several populations studied, branches were shorter in the southeastern sectors of the crown, reducing self-shading early in the morning. Measurements of direct beam radiation interception by detached branches, using digital image processing, indicated that foliage clusters oriented toward the southeast exhibited less self-shading during spring mornings than clusters oriented northeast. This effect was not apparent at the summer solstice. This type of canopy architecture may tend to minimize self-shading during the morning hours when conditions are more favorable for photosynthesis, resulting in an improved daily water use efficiency.     

The taxonomic status of "Halobacterium marismortui" from the Dead Sea: a comparison with Halobacterium vallismortis

A Halobacterium strain, isolated by Ginzburg et al. from the Dead Sea in the late 1960's, often referred to as "Halobacterium marismortui" or "Halobacterium of the Dead Sea" (deposited in the American Type Culture Collection as ATCC 43049) was compared with Halobacterium (Haloarcula) vallismortis ATCC 29715. The strains appeared to be very closely related, as shown by the near identity of their 5S and 16S ribosomal RNA's, and a large number of other common properties. Distinct differences exist, however, in cell morphology, and in their potency to utilize different sugars and other compounds.     

Enhanced binding of a 95 kDa protein to p53 in cells undergoing p53-mediated growth arrest.

To explore the biochemical functions of p53, we have initiated a search for cellular p53-binding proteins. Coprecipitation of three polypeptides was observed when cell lines overexpressing a temperature-sensitive (ts) p53 mutant were maintained at 32.5 degrees C (wild-type p53 activity, leading to growth arrest) but not at 37.5 degrees C (mutant p53 activity). One of these three proteins, designated p95 on the basis of its apparent molecular mass, was highly abundant in p53 immune complexes. We demonstrate herein that p95 is a p53-binding protein, which exhibits poor p53-binding in cells overproducing several distinct mutant p53 proteins. Yet, p95 associates equally well with both the wild-type (wt) and the mutant conformations of the ts p53 in transformed cells growth-arrested at 32.5 degrees C. On the basis of our findings we suggest that wt p53 activity increases p53-p95 complex formation and that such interaction may play a central role in p53 mediated tumour suppression.     

Identification of a minimal transforming domain of p53: negative dominance through abrogation of sequence-specific DNA binding.

Mutations in the p53 gene are most frequent in cancer. Many p53 mutants possess transforming activity in vitro. In cells transformed by such mutants, the mutant protein is oligomerized with endogenous cell p53. To determine the relevance of oligomerization for transformation, miniproteins containing C-terminal portions of p53 were generated. These miniproteins, although carrying no point mutation, transformed at least as efficiently as full-length mutant p53. Transforming activity was coupled with the ability to oligomerize with wild-type p53, as well as with the ability to abrogate sequence-specific DNA binding by coexpressed wild-type p53. These findings suggest that p53-mediated transformation may operate through a dominant negative mechanism, involving the generation of DNA binding-incompetent oligomers.     

Simian virus 40 can overcome the antiproliferative effect of wild-type p53 in the absence of stable large T antigen-p53 binding.

In simian virus 40 (SV40)-transformed cells, a tight complex is formed between the viral large T antigen (large T) and p53. It has been proposed that this complex interferes with the antiproliferative activity of p53. This notion was tested in primary rat fibroblasts by assessing the ability of SV40-mediated transformation to be spared from the inhibitory effect of wild-type (wt) p53. The data indicate that relative to transformation induced by myc plus ras, SV40-plus-ras-mediated focus formation was indeed much less suppressed by p53 plasmids. A majority of the resultant cell lines made a p53 protein with properties characteristic of a wt conformation. Furthermore, cell lines expressing stably both SV40 large T and a temperature-sensitive p53 mutant continued to proliferate at a temperature at which this p53 assumes wt-like properties and normally causes a growth arrest. Surprisingly, at least partial resistance to the growth-inhibitory effect of wt p53 was also evident when transformation was mediated by an SV40 deletion mutant, encoding a large T which does not bind p53 detectably. In addition to supporting the idea that SV40 can overcome the growth-restrictive activity of wt p53, these findings strongly suggest that at least part of this effect does not require a stable association between p53 and large T.     

Induction of growth arrest by a temperature-sensitive p53 mutant is correlated with increased nuclear localization and decreased stability of the protein.

A temperature-sensitive mutant of p53, p53Val-135, was found to be able to arrest cell proliferation when overexpressed at 32.5 degrees C. While much of the protein was cytoplasmic in cells proliferating at 37.5 degrees C, it became predominantly nuclear at 32.5 degrees C. Concomitantly, p53Val-135 became destabilized, although not to the extent seen in primary fibroblasts.     

Distribution of Hydrogen-Metabolizing Bacteria in Alfalfa Field Soil

H₂ evolved by alfalfa root nodules during the process of N₂ fixation may be an important factor influencing the distribution of soil bacteria. To test this hypothesis under field conditions, over 700 bacterial isolates were obtained from fallow soil or from the 3-mm layer of soil surrounding alfalfa (Medicago sativa L.) root nodules, alfalfa roots, or bindweed (Convolvulus arvensis L.) roots. Bacteria were isolated under either aerobic or microaerophilic conditions and were tested for their capacity to metabolize H₂. Isolates showing net H₂ uptake and ³H₂ incorporation activity under laboratory conditions were assigned a Hup⁺ phenotype, whereas organisms with significant H₂ output capacity were designated as a Hout⁺ phenotype. Under aerobic isolation conditions two Hup⁺ isolates were obtained, whereas under microaerophilic conditions five Hup⁺ and two Hout⁺ isolates were found. The nine isolates differed on the basis of 24 standard bacteriological characteristics or fatty acid composition. Five of the nine organisms were isolated from soil around root nodules, whereas the other four were found distributed among the other three soil environments. On the basis of the microaerophilic isolations, 4.8% of the total procaryotic isolates from soil around root nodules were capable of oxidizing H₂, and 1.2% could produce H₂. Two of the Hup⁺ isolates were identified as Rhizobium meliloti by root nodulation tests, but the fact that none of the isolates reduced C₂H₂ under the assay conditions suggested that the H₂ metabolism traits were associated with various hydrogenase systems rather than with nitrogenase activity. Results from this study support the concept that H₂ evolution by alfalfa root nodules has a significant effect on the surrounding microenvironment and influences the number and diversity of bacteria occupying that region.