The rate of nutrient release from grass and dung following immersion in lake water

Summary Two experiments were carried out to determine the rate of release of ions to lake water from dry grass (largely Eragrostis species) and dung from elephant, impala and buffalo. The ions released most rapidly were PO₃ ^3- and K⁺, followed by NO₃ ^- and Ca²⁺ + Mg²⁺; the smallest increase was shown by Na⁺. In general, dung derived from grass released ions more rapidly than grass itself; the results are discussed in relation to ash analyses of grass and dung. The possible importance to Lake Kariba of the nutrients released by grass and dung following immersion under natural conditions is considered.

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Résumé On a procédé à la réalisation de deux expériences visant à déterminer la vitesse de libération des ions dans l'eau d'un lac à partir d'herbe sèche (appartenant principalement à l'espèce Eragrostis) et de crottin d'éléphant, d'impala et de buflle. Par ordre décroissant, on mesure les vitesses de libération des ions les plus grands pour PO₄ ^3- et K⁺, et ensuite pour NO₃ ^- et Ca²⁺ + Mg²⁺; Na⁺ manifeste l'augmentation de concentration la plus faible. En règle générale, le crottin formé à partir d'herbe a libéré les ions à vitesse plus grande que l'herbe elle-même; les résultats sont interprétés par rapport à des analyses de cendre d'herbe et de crottin. On a cherché à estimer l'importance que peuvent présenter, pour le lac Kariba, la libération de ces éléments nutritifs après immersion dans des conditions naturelles.

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Present address: Biology Department, Chancellor College, University of Malawi, Limbe, MalawiN     

A single 10-residue pre-S(1) peptide can prime T cell help for antibody production to multiple epitopes within the pre-S(1), pre-S(2), and S regions of HBsAg

The purpose of this study was to identify and characterize T cell and B cell recognition sites within the pre-S(1) region of HBsAg/p43, and to then analyze functional T cell-B cell interactions at the level of in vivo antibody production. The results indicate: three peptide sequences within the pre-S(1) region of HBsAg were identified which can induce and elicit HBsAg/p43-specific T cell proliferation; a 10-amino acid peptide, p12-21, defines one pre-S(1)-specific T cell recognition site, and residues 18 and 19 are critical to the recognition process; the p12-21 sequence can function as a T cell carrier for a synthetic B cell epitope within the pre-S(2) region; the p94-117 sequence contains at least two T cell recognition sites; five distinct, pre-S(1)-specific antibody binding sites were identified; synthetic pre-S(1) region T cell determinants can prime in vivo antibody production to multiple B cell epitopes within the pre-S(2) and S regions, as well as within the pre-S(1) region; the specificity of the primed T cell population can influence the specificity of the B cell response; and T cell recognition of pre-S(1) region peptides is regulated by H-2-linked genes.     

Total and poly(A) RNA yields during an aluminum encephalopathy in rabbit brains

The yields of total and poly(A) RNA were examined in rabbit forebrains during an experimentally induced aluminum encephalopathy. Rabbits (35 day old) were injected intracranially with 13 mole Al lactate and sacrificed 1, 3, 7, 10, or 12 days later. IRNA yields (total RNA minus transfer RNA) were not significantly altered during the encephalopathy. Poly(A) RNA yields, assayed by oligo(dT)-cellulose fractionation and by a [³H]poly(U) hybridization assay on IRNA, were increased significantly by the end of the asymptomatic stage of the encephalopathy (7 days post-Al injection). The increase in messenger RNA population may represent either a compensatory response to cell damage induced by aluminum or the accumulation of messager RNA for proteins directly related to the expression of aluminum toxicity.     

Evidence for a repeating cross-beta sheet structure in the adenovirus fibre

The amino acid sequence of the adenovirus fibre protein reveals an approximately repeating motif of 15 residues. A diagonal comparison matrix established that these repeats extended from residue 43 to residue 400 of the 581 residue sequence. Assignment of secondary structure combined with model building showed that each 15-residue segment contained two short beta-strands and two beta-bends, one of which incorporated an extra residue in a beta-bulge of the Gx type. The 44 strands together gave a long (210 A) narrow, amphipathic beta-sheet, which could be stabilised by dimer formation to give the shaft of the fibre. The knob could arise from a dimer of the C-terminal 180 residue segment, predicted to be an 8-10 stranded beta-sandwich. This model is consistent with the electron micrographs of the fibre and it was supported by measurements of c.d. and of electron diffraction from microcrystals. The latter gave a pair of wide angle arcs, corresponding to a repeat of 4.7 A, oriented appropriately for a cross-beta structure. The relation of this structure to globular structures is discussed and a folding pathway is proposed. In its general features the structure resembles that proposed for the tail fibre of bacteriophage T4.     

Changes in Chromatin Structure Associated with Alzheimer's Disease

Abstract— The enzyme micrococcal nuclease was used to examine the accessibility of chromatin extracted from brains of 13 patients with senile and presenile dementia of the Alzheimer type. Compared with chromatin extracted from brains of 8 patients without neurological signs or brain pathology and brains of 7 patients with nonAlzheimer dementia, Alzheimer chromatin was less accessible to this enzyme-. Reduced accessibility was reflected by a reduced yield of mononucleosomes in comparison with dinucleosomes and larger oligomers. Both neuronal and glial chromatin were found to be similarly affected. The reduced yield of mononucleosomes from Alzheimer chromatin is not due to their increased breakdown, but is probably related to protein associated with the internucleosomal linker region that retards nuclease action. Dinucleosomes isolated from control and Alzheimer nuclease digests were examined for their protein complement. Three perchloric acid-soluble proteins situated in the histone HI region of sodium dodecyl sulfate (SDS) gels were present in elevated levels in Alzheimer dinucleosomes. These results represent the first example of altered chromosomal proteins associated with a diseased state of the brain.     

Survival strategies in tropical rain pools

Summary Adaptations of three larval diptera in central Africa, each inhabiting rain-filled rock pools of characteristic duration, have been studied by field observation and experiment.The duration of the pool is important in determining which of the three species is present. Large pools, lasting a few weeks after each rain, favour Chironomus imicola which has a larval life span of as little as twelve days. This species relies on egg laying female flies to re-invade newly filled pools. In cases where the pool lasts for a shorter time than the minimum larval life span a mechanism is needed to survive dry periods in situ. Such pools are inhabited by larvae of Polypedilum vanderplanki and Dasyhelea thompsoni. Larvae of P. vanderplanki are poor at invading newly flooded pools and are also poor at competing with other species. However they are able to tolerate virtually a complete loss of body water and are therefore able to survive drought in the dry mud. They are consequently always the first there after refilling, a factor that provides them with sufficient advantage to eventually become established in very small pools. D. thompsoni larvae, not quite so good at surviving drought, but better at invading, occupy pools of intermediate size. They probably inhabit a larger number of pools than either of the other two species.A hazard associated with surviving dry phases in situ is vulverability to attack by terrestrial scavengers. However the activity of scavengers such as pheidolid ants, although conspicuous, is confined to periods when standing water has evaporated but the mud is still moist. Once dry, predation stops. Losses from this cause are therefore likely to be associated with periodic dry phases throughout the rainy season rather than with the dry season itself.     

Tests for comparing related amino-acid sequences. Cytochrome c and cytochrome c 551

An improved method for testing similarities or repeats in protein sequences is described. It includes three features: a measure of similarity for amino acids, based on observed substitutions in homologous proteins; a search procedure which compares all pairs of segments of two proteins; new statistical tests which estimate the probabilities that observed correlations could have occurred by chance. Calculations show that gene duplication has probably not occurred in plant ferredoxins; phage Qβ and f2 coat proteins may be homologous; and repeats in cytochrome c are not statistically significant. The method predicted an alignment of cytochrome c and c₅₅₁ sequences which later appeared consistent with Dickerson's atomic model of horse cytochrome c.     

Cloning and expression of a human muscle phosphofructokinase cDNA

The nucleotide sequence of a 2.86-kb cDNA clone containing the complete human muscle phosphofructokinase (PFK) protein-coding region was determined. It comprises 76 bp of 5'-untranslated sequence, 2340 bp encoding human muscle PFK polypeptide, and 399 bp of 3'-untranslated sequence plus a poly(A) tract. A retroviral vector was utilized to express the product of this coding sequence in mouse fibroblasts. The PFK-coding cDNA was shown to code for an enzymatically active polypeptide by immunoprecipitation analysis and DEAE-Sephadex A-25 chromatography.     

Effects of Fluorescent Brighteners on Growth and Morphology of the Red Alga Antithamnion Kylinii

Four fluorescent brighteners (Fluorescent Brightener 28, Fluostain I, Fluostain II and Cellufluor) were examined with respect to their binding affinity, toxicity (their ability to stunt growth), and teratogenic effects on the red alga Antithamnion kylinii. Maximum binding occurred with FB-28 and F-II but these stains showed the greatest inhibition of growth when plants were exposed to concentrations of 0.01% for 30 min. Filaments incubated in low stain concentrations (0.0005%) showed cell abnormalities with all stain types, with FB-28 producing the most extreme deformations of both intercalary and apical cells. The experiments suggest that extensive experimentation is required to develop protocols for vital cell wall stains that minimize toxicity and maximize binding.