Structure of dimeric SecA, the Escherichia coli preprotein translocase motor

SecA is the preprotein translocase ATPase subunit and a superfamily 2 (SF2) RNA helicase. Here we present the 2 A crystal structures of the Escherichia coli SecA homodimer in the apo form and in complex with ATP, ADP and adenosine 5'-[beta,gamma-imido]triphosphate (AMP-PNP). Each monomer contains the SF2 ATPase core (DEAD motor) built of two domains (nucleotide binding domain, NBD and intramolecular regulator of ATPase 2, IRA2), the preprotein binding domain (PBD), which is inserted in NBD and a carboxy-terminal domain (C-domain) linked to IRA2. The structures of the nucleotide complexes of SecA identify an interfacial nucleotide-binding cleft located between the two DEAD motor domains and residues critical for ATP catalysis. The dimer comprises two virtually identical protomers associating in an antiparallel fashion. Dimerization is mediated solely through extensive contacts of the DEAD motor domains leaving the C-domain facing outwards from the dimerization core. This dimerization mode explains the effect of functionally important mutations and is completely different from the dimerization models proposed for other SecA structures. The repercussion of these findings on translocase assembly and catalysis is discussed.     

Ovarian activity and plasma sex steroid levels of Distichodus antonii in relation to environmental conditions in the upper basin of the Congo River

Distichodus antonii is an endemic fish species of the Congo River basin in which the stocks of wild populations are threatened by overfishing pressure. Knowledge of its reproductive biology would be useful in consideration of conservation and management options for the species. Therefore, this study investigated changes in ovarian activity and levels of steroid profiles in wild populations in relation to variation in temperature and rainfall. Adult females (n = 101, body weight of 3 183 ± 14.75 g, SE) were captured monthly over one year (2013–2014). Apart from evaluation of oocyte diameters and gonad developmental stages, gonado-, hepato-, lipososomatic indices (GSI, HSI, LSI) and plasma levels of sex steroids (testosterone-T, estradiol-17β-E2) were determined. The results suggested a synchronous development of oocytes with two annual reproductive seasons over the one-year study. Plasma T and E2 levels peaked during spawning periods likely reflecting active oogenesis. The highest values of morphosomatic indices were observed during the longest rainfall period in September, and were associated with high steroidogenic activity evidenced by increased E2 production. In addition, more vitellogenic oocytes (September and October) were observed during the latter season than during the short rainy season (in May).     

A new scale for the assessment of wheat spike morphogenesis

The period prior to anthesis determines to a great extent the yield in wheat by modifying the number of fertile florets and hence the number of grains per spike. For an easy and accurate identification of this period to researchers and cereal growers a simple numerical scale of wheat spike development is proposed. It includes 20 distinct stages, starting from the apex transition stage and ending just prior to heading, with the stages being separated by similar‐sized steps in thermal time to produce a continuous scale. The scale describes the whole process of wheat apical development and is convenient (e.g. uses easily detectable characters without great magnification, such as the development of awns, lemmas and glumes) and precise (e.g. uses combination of more stable characters, such as pistil and stamen development as well as the sequence of floret initiation, in order to accurately assess the development of the spike). The proposed scale was used to describe the development of the durum wheat cultivar “Mexicali 81” during two seasons. The meteorological conditions during the different cultivation seasons affected the onset and the duration of the spike developmental phases. Additionally, a variation was observed concerning the synchronisation between spike morphogenesis and plant external developmental phases (e.g. tillering, jointing and boot). The advantages of the new scale with respect to the already existing ones are discussed.     

AIR: A batch-oriented web program package for construction of supermatrices ready for phylogenomic analyses

Background  

Large multigene sequence alignments have over recent years been increasingly employed for phylogenomic reconstruction of the eukaryote tree of life. Such supermatrices of sequence data are preferred over single gene alignments as they contain vastly more information about ancient sequence characteristics, and are thus more suitable for resolving deeply diverging relationships. However, as alignments are expanded, increasingly numbers of sites with misleading phylogenetic information are also added. Therefore, a major goal in phylogenomic analyses is to maximize the ratio of information to noise; this can be achieved by the reduction of fast evolving sites.     

Invasion status of Florida bass Micropterus floridanus (Lesueur, 1822) in South Africa

Largemouth bass Micropterus salmoides are a popular North American angling species that was introduced into South Africa in 1928. To enhance the largemouth bass fisheries, Florida bass Micropterus floridanus were introduced into KwaZulu Natal, South Africa, in 1980. Knowledge on the status of M. floridanus in South Africa is required, because it lives longer and reaches larger sizes than M. salmoides, which may result in heightened impacts on native biota. Because M. floridanus are morphologically similar, but genetically distinct from M. salmoides, the distribution of this species was assessed by genetically screening 185 Micropterus sp. individuals sampled from 20 localities across South Africa using the mitochondrial ND2 gene. Individuals with mitochondrial DNA matching M. salmoides were recovered from 16 localities, whereas M. floridanus mitochondrial DNA was recovered from 13 localities. At nine localities (45%), the mitochondrial DNA of both species was detected. These results demonstrate M. floridanus dispersal to multiple sites across South Africa.     

The influence of temperature, photoperiod and plant type on the predation rate of Macrolophus pygmaeus on Myzus persicae

The effect of temperature and photoperiod on the rate of predation of nymphs and adults of the predator Macrolophus pygmaeus was studied using Myzus persicae prey feeding on egg-plant and pepper plants. The experiments were conducted at three photoperiods (16L:8D, 12L:12D and 8L:16D), three temperatures (20, 25 and 30 °C), and at 65% r.h. The rate of predation increased with temperature. Predation rate was affected by photoperiod on pepper but not on egg-plant. Females and fifth instar nymphs were the most voracious stages followed by third and fourth instar nymphs and males. First and second instar nymphs consumed far fewer aphids. Predation rate was higher on leaves of pepper than egg-plant, especially at 30 °C. Variation in the efficacy of this predator is discussed.     

A new quantitative polymerase chain reaction-high performance ion exchange liquid chromatographic method for the detection of fibroblast growth factor-beta (FGF-beta) gene amplification.

A method for the quantitative determination of fibroblast growth factor-beta (FGF-beta) genomic amplification based on the use of optimized polymerase chain reaction (PCR) procedures and high performance ion exchange (HPIEX) liquid chromatography has been developed. Co-amplification of a second genomic species permits internal standardization of the techniques during optimization of the reaction conditions, the PCR cycle number and the PCR cycle efficiency, as well as during the analytical HPIEX chromatographic determination of the PCR products. These investigations confirm the versatility of these procedures to quantitatively analyse FGF-beta gene amplification in various cells and tissues.     

Ethylene enhances shoot formation in cultures of the peach rootstock GF-677 (Prunus persica x P. amygdalus)

The influence of ethylene on shoot formation from GF-677 (Prunus persica × P. amygdalus) shoot tip explants was studied in vitro. Cultures in test tubes were placed inside 5 1 glass jars and supplemented with various ethylene concentrations (0–10 ppm). Ethylene at 0.1 ppm, applied during the first 2 weeks of culture, increased the number and the length of shoots produced in vitro. Test tubes with cultures sealed with various types of closure accumulated in their atmosphere different levels of ethylene ranging from 0.1 to 1.2 ppm, depending on the type of closure. Test tubes with cotton-wool bungs had the least while those with serum stoppers had the highest amount of ethylene. The maximum number of shoots was recorded in test tubes covered with serum stoppers. The ethylene concentration was related linearly (R=0.974) to the shoot number and exponentially (R=0.975) to the shoot length.Abbreviations BA benzyladenine - IAA indoleacetic acid - HSD honestly significant difference