			Home About us Contact

Element Activities (element + activity)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Mineralogy, Lithogeochemistry and Elemental Mass Balance of the Hydrothermal Alteration Associated with the Gold-rich Batu Hijau Porphyry Copper Deposit, Sumbawa Island, Indonesia

RESOURCE GEOLOGY, Issue 3 2009
Arifudin Idrus
Abstract This paper discusses the mineralogy, whole-rock geochemistry and elemental mass balance of the hydrothermal alteration zones within the Batu Hijau porphyry copper-gold deposit, Sumbawa Island, Indonesia. The hydrothermal alteration and mineralisation developed in four stages, namely (i) the early stage consisting of a central copper-gold-bearing biotite (potassic), proximal actinolite (inner propylitic) and the distal chlorite-epidote (outer propylitic) zones; (ii) the transitional stage represented by the chlorite-sericite (intermediate argillic) zone; (iii) the late stages distinguished into the sericite-paragonite (argillic) and pyrophyllite-andalusite (advanced argillic) zones; and (iv) the very late stage typified by the illite-sericite zone. In general, major elements (particularly Ca, Mg, Na and K) and some minor and rare earth elements decrease from the least altered rocks towards the late alteration zones as a consequence of the breakdown of Ca-bearing hornblende, biotite and plagioclase. Chemical discrimination by means of millicationic R1 -R2 diagram indicates that R1 [4Si , 11(Na + K) , 2(Fe + Ti)] increases while R2[6Ca + 2Mg + Al] decreases with increasing alteration intensity, from least-altered, through early, transitional, to late alteration zones. Rare earth elements-chondrite (C1) normalised patterns also exhibit the depletion of the elements through the subsequent alteration zones. These results are consistent with the elemental mass balance calculation using the isocon method which shows that the degree of mass and volume depletion systematically increases during alteration. A decrease of the elements as well as mass and volume from early, through transitional to late alteration stages may imply a general decrease of the element activities in hydrothermal fluids during the formation of the alteration zones. [source]

A detailed look at 7 million years of genome evolution in a 439 kb contiguous sequence at the barley Hv-eIF4E locus: recombination, rearrangements and repeats

THE PLANT JOURNAL, Issue 2 2005
Thomas Wicker
Summary Six overlapping BAC clones covering the Hv-eIF4E gene region in barley were sequenced in their entire length, resulting in a 439.7 kb contiguous sequence. The contig contains only two genes, Hv-eIF4E and Hv-MLL, which are located in a small gene island and more than 88% of the sequence is composed of transposable elements. A detailed analysis of the repetitive component revealed that this chromosomal region was affected by multiple major duplication and deletion events as well as the insertion of numerous transposable elements, resulting in a complete reshuffling of genomic DNA. Resolving this highly complex pattern resulted in a model unraveling evolutionary events that shaped this region over an estimated 7 million years. Duplications and deletions caused by illegitimate recombination and unequal crossing over were major driving forces in the evolution of the Hv-eIF4E region, equaling or exceeding the effects of transposable element activities. In addition to a dramatic reshuffling of the repetitive portion of the sequence, we also found evidence for important contributions of illegitimate recombination and transposable elements to the sequence organization of the gene island containing Hv-eIF4E and Hv-MLL. [source]

THE FITNESS EFFECTS OF SPONTANEOUS MUTATIONS IN CAENORHABDITIS ELEGANS

EVOLUTION, Issue 4 2000
Larissa L. Vassilieva
Abstract. Spontaneous mutation to mildly deleterious alleles has emerged as a potentially unifying component of a variety of observations in evolutionary genetics and molecular evolution. However, the biological significance of hypotheses based on mildly deleterious mutation depends critically on the rate at which new mutations arise and on their average effects. A long-term mutation-accumulation experiment with replicate lines of the nematode Caenorhabditis elegans maintained by single-progeny descent indicates that recurrent spontaneous mutation causes approximately 0.1% decline in fitness per generation, which is about an order of magnitude less than that suggested by previous studies with Drosophila. Two rather different approaches, Bateman-Mukai and maximum likelihood, suggest that this observation, along with the observed rate of increase in the variance of fitness among lines, is consistent with a genomic deleterious mutation rate for fitness of approximately 0.03 per generation and with an average homozygous effect of approximately 12%. The distribution of mutational effects for fitness appears to have a relatively low coefficient of variation, being no more extreme than expected for a negative exponential, and for one composite fitness measure (total progeny production) approaches constancy of effects. These results are derived from assays in a benign environment. At stressful temperatures, estimates of the genomic deleterious mutation rate (for genes expressed at such temperatures) is sixfold lower, whereas those for the average homozygous effect is approximately eightfold higher. Our results are reasonably compatible with existing estimates for flies, when one considers the differences between these species in the number of germ-line cell divisions per generation and the magnitude of transposable element activity. [source]

Functional analysis of the sea urchin-derived arylsulfatase (Ars)-element in mammalian cells

GENES TO CELLS, Issue 9 2006
Satoshi Watanabe
An insulator is a DNA sequence that has both enhancer-blocking activity, through its ability to modify the influence of neighboring cis -acting elements, and a barrier function that protects a transgene from being silenced by surrounding chromatin. Previously, we isolated and characterized a 582-bp-long element from the sea urchin arylsulfatase gene (Ars). This Ars -element was effective in sea urchin and Drosophila embryos and in plant cells. To investigate Ars -element activity in mammalian cells, we placed the element between the cytomegalovirus enhancer and a luciferase (luc) expression cassette. In contrast to controls lacking the Ars -element, NIH3T3 and 293T cells transfected with the element-containing construct displayed reduced luciferase activities. The Ars -element therefore acts as an enhancer-blocking element in mammalian cells. We assessed the barrier activity of the Ars -element using vectors in which a luc expression cassette was placed between two elements. Transfection experiments demonstrated that luc activity in these vectors was approximately ten-fold higher than in vectors lacking elements. Luc activities were well maintained even after 12 weeks in culture. Our observations demonstrate that the Ars -element has also a barrier activity. These results indicated that the Ars -element act as an insulator in mammalian cells. [source]