A genetic approach to the identification of functional amino acids in protein p6 of Bacillus subtilis phage ?29

Protein p6 of the Bacillus subtilis phage ø29 is essential for in vivo viral DNA replication. This protein activates the initiation of ø29 DNA replication in vitro by forming a multimeric nucleoprotein complex at the replication origins. The N-terminal region of protein p6 is involved in DNA binding, as shown by in vitro studies with p6 proteins altered by deletions or missense mutations. We report on the development of an in vivo functional assay for protein p6. This assay is based on the ability of protein p6-producing B. subtilis non-suppressor (su ^–) cells to support growth of a ø29 sus6 mutant phage. We have used this trans-complementation assay to investigate the effect on in vivo viral DNA synthesis of missense mutations introduced into the protein p6 N-terminal region. The alteration of lysine to alanine at position 2 resulted in a partially functional protein, whereas the replacement of arginine by alanine at position 6 gave rise to an inactive protein. These results indicate that arginine at position 6 is critical for the in vivo activity of protein p6. Our complementation system provides a useful genetic approach for the identification of functionally important amino acids in protein p6.     

The barbs (Barbus spp.) of Lake Tana: a forgotten species flock?

Synopsis All living species occupy an ecological niche, and are positioned within a trophic hierarchy. Extinct organisms presumably held similar behavioral and coevolutionary characteristics in the past, and were susceptible to the same kinds of natural ecological pressures operating today. Paleoecological investigations are limited by the incompleteness of the fossil record, and particularly by a lack of behavioral data that are so fundamental to ecological studies of living communities and habitats. Opportunities to examine the coevolutionary structure of ancient communities from empirical data are extremely rare. One such opportunity is provided by the Lower Cretaceous Santana Formation of north-eastern Brazil, a series of richly fossiliferous strata approximately 110 million years old. Many fossil fishes from the Santana Formation contain identifiable prey, including decapod crustaceans and fishes. A trophic hierarchy of these organisms is reconstructed here, and their ecological relationships are discussed. Comparison is made with a similar fish fauna from the Upper Jurassic Solnhofen Limestone of Germany. Low-level, intermediate and high-level predators are identified in each fauna. Predator-prey relationships in the Santana fauna are strongly hierarchical, and are more focussed at the intermediate predator level than in Solnhofen. Comparison with a model of predator-prey relationships between fishes and benthic fauna of the Baltic Sea (which like the Araripe Basin represents a semi-enclosed environment) suggests that heavy predation on teleosts such asRhacolepis, occupying an intermediate trophic level, may have permitted benthic decapods to proliferate and exclude other benthic organisms. Less intense predation on fishes at the intermediate trophic level would allow their numbers to increase, thereby increasing the intensity of predation on the benthos at the base of the trophic hierarchy.     

Self-fertility and associated flower head traits in the Iberian taxa ofLactuca and related genera (Asteraceae: Lactuceae)

Sexual reproduction is the main reproduction mechanism among the 14 wild Iberian taxa ofLactuca, Prenanthes, Cicerbita, andMycelis. High levels of self-fertilization occur inLactuca, as well as facultative and obligate xenogamy. Xenogamy is strongly correlated with large capitula having blue or bright yellow colouration, high P/O ratios, and long anthesis, whereas self-fertilization is correlated with smaller capitula having pale yellow colouration, small P/O ratios, and short anthesis. Large variations occur in P/O index among taxa showing similar fertilization mechanism, probably in relation to the number of florets included in flower heads. Interesting differences in reproductive systems have been detected between subspecies ofLactuca viminea.     

A descriptive study of some Antarctic notaspidean opisthobranchs (Gastropoda), with description of a new genus and species

During the expedition “ANTARTIDA 9101”, organized by the Spanish Oceanographic Institute to the South Orkney Islands, four specimens of notaspidean gastropods were collected. Three of them have been identified as Bathyberthella antarctica Willan and Bertsch, 1987. However, one specimen, although externally similar to B. antarctica, had an internal anatomy exhibiting features that have enabled us to consider it to be a new genus and species. This new taxon is characterized by the presence of jaws without mandibular elements, and a vaginal gland that partially surrounds the distal region of the vaginal duct. In this paper the new genus and species is described. Additional anatomical data of the specimens of B. antarctica collected during the expedition are also included.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Latency of cathepsin B secreted by human colon carcinoma cells is not linked to secretion of cystacin C and is relieved by neutrophil elastase

The lysosomal cystein proteinase cathepsin B is shown to be secreted by ten human colon carcinoma cell lines and to accumulate in culture media as a latent enzyme. The cell lines also secrete a physiological inhibitor of cathepsin B, cystatin C. A significant correlation was found between secretion of the latent enzyme and the inhibitor (r = 0.755, P < 0.01). The aim of the present study was to modulate the respective secretion of the two antagonists to test whether or not latency of cathepsin B was due to the concomitant secretion of the inhibitor. SW480 colon carcinoma cells were treated with the acidotropic agent ammonium chloride, phorbol 12-myristate 13-acetate, and the inflammatory cytokines TGF-β, TNF-α, and IL-1β. Ammonium chloride significantly increased latent cathepsin B levels without affecting the constitutive secretion of cystatin C. Phorbol 12-myristate 13-acetate induced a 4- to 5-fold increase in secreted latent cathepsin B, but did not alter significantly the accumulation of cystatin C in media. The cytokines, TGF-β, TNF-α, and IL-1β, had no major effect on the expression of these two antagonists. Latent cathepsin B released from human carcinoma cells could be efficiently activated by neutrophil elastate at neutral pH. It is concluded that latent cathepsin B is a true proenzyme rather than an enzyme-inhibitor comples. In addition, our data from neutrophil elastate activation experiments indicate that a proteolytic system for activation of the tumor cell-secreted latent enzyme may exist in vivo.     

Experimental evaluation of the foliar flag hypothesis using fruits of Rhus glabra (L.)

I tested experimentally whether the presence of colorful plastic ovals (simulating foliar flags) attached to infructescences of Rhus glabra increase fruit removal by birds in a forest-oldfield border. I used a factorial experimental design testing for the effect of size (small or large) and color (yellow or red) of the flags. There was also a control, without flags. Large red flags increased the percent of fruits removed from the panicles, but yellow and small flags had no effect. My results give partial support to Stiles (1982) hypothesis that early color change of leaves close to the fruits in some plants may serve as visual signals that attract frugivorous birds and enhances seed dispersal.     

Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium

We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (V_max) of the system was 3.86 units (U) mg^–1 protein with arabinoxylan as substrate and the substrate concentration giving half V_max (S_0.5) was 0.52 mg ml^–1. At concentrations of arabinoxylan greater than 15 mg ml^–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components. Correspondence to: P. Broda     

Demography and social structure of one group of muriquis (Brachyteles arachnoides)

We monitored one group of muriquis, or woolly spider monkeys (Brachyteles arachnoides), over a 9-year period at Fazenda Montes Claros, Minas Gerais, Brazil. The group grew from 22 to 42 individuals due to the births of 21 surviving infants. Eight immigrations involving immature females were offset by emigrations and disappearances. The home range of the group expanded as the group size increased. The group traveled as a cohesive unit during the first 6 years of the study, but recently it has begun to show greater tendencies to fission temporarily into smaller subgroups. Six adult males from the other muriqui group at this site have simultaneously increased their associations with the main study group. These observations indicate that the group is in a state of transition which may lead, ultimately, either to its division into two smaller units or to a more fluid social structure.     

Inhibition of penicillin biosynthetic enzymes by halogen derivatives of phenylacetic acid

Summary The effect of phenylacetic acid (PAA) and several analogs on the activity of isopenicillin N synthase (IPNS) and acyl-CoA: 6-APA acyltransferase (AT) fromPenicillium chrysogenum Wis 54-1255 has been tested. Whereas the substitution on the ring of a hydrogen atom by hydroxy-, methyl- or methoxy- groups did not cause any effect, the presence of halogens (Cl or Br) at positions 3 and/or 4 of PAA strongly inhibited these two enzymes. The replacement of hydrogen atoms by fluorine in certain positions also caused inhibition, but to a lesser extent.