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Eukaryotic Organelles (eukaryotic + organelle)

Distribution by Scientific Domains
Life Sciences75%

Selected Abstracts

Evolution and persistence of the cilium

CYTOSKELETON, Issue 12 2007
Peter Satir
Abstract The origin of cilia, a fundamental eukaryotic organelle, not present in prokaryotes, poses many problems, including the origins of motility and sensory function, the origins of nine-fold symmetry, of basal bodies, and of transport and selective mechanisms involved in ciliogenesis. We propose the basis of ciliary origin to be a self-assembly RNA enveloped virus that contains unique tubulin and tektin precursors. The virus becomes the centriole and basal body, which would account for the self-assembly and self-replicative properties of these organelles, in contrast to previous proposals of spirochaete origin or endogenous differentiation, which do not readily account for the centriole or its properties. The viral envelope evolves into a sensory bud. The host cell supplies the transport machinery and molecular motors to construct the axoneme. Polymerization of cytoplasmic microtubules in the 9 + 0 axoneme completes the 9 + 2 pattern. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source]

Genetic and functional properties of uncultivated thermophilic crenarchaeotes from a subsurface gold mine as revealed by analysis of genome fragments

ENVIRONMENTAL MICROBIOLOGY, Issue 12 2005
Takuro Nunoura
Summary Within a phylum Crenarchaeota, only some members of the hyperthermophilic class Thermoprotei, have been cultivated and characterized. In this study, we have constructed a metagenomic library from a microbial mat formation in a subsurface hot water stream of the Hishikari gold mine, Japan, and sequenced genome fragments of two different phylogroups of uncultivated thermophilic Crenarchaeota: (i) hot water crenarchaeotic group (HWCG) I (41.2 kb), and (ii) HWCG III (49.3 kb). The genome fragment of HWCG I contained a 16S rRNA gene, two tRNA genes and 35 genes encoding proteins but no 23S rRNA gene. Among the genes encoding proteins, several genes for putative aerobic-type carbon monoxide dehydrogenase represented a potential clue with regard to the yet unknown metabolism of HWCG I Archaea. The genome fragment of HWCG III contained a 16S/23S rRNA operon and 44 genes encoding proteins. In the 23S rRNA gene, we detected a homing-endonuclease encoding a group I intron similar to those detected in hyperthermophilic Crenarchaeota and Bacteria, as well as eukaryotic organelles. The reconstructed phylogenetic tree based on the 23S rRNA gene sequence reinforced the intermediate phylogenetic affiliation of HWCG III bridging the hyperthermophilic and non-thermophilic uncultivated Crenarchaeota. [source]

Optimal observability of sustained stochastic competitive inhibition oscillations at organellar volumes

FEBS JOURNAL, Issue 1 2006
Kevin L. Davis
When molecules are present in small numbers, such as is frequently the case in cells, the usual assumptions leading to differential rate equations are invalid and it is necessary to use a stochastic description which takes into account the randomness of reactive encounters in solution. We display a very simple biochemical model, ordinary competitive inhibition with substrate inflow, which is only capable of damped oscillations in the deterministic mass-action rate equation limit, but which displays sustained oscillations in stochastic simulations. We define an observability parameter, which is essentially just the ratio of the amplitude of the oscillations to the mean value of the concentration. A maximum in the observability is seen as the volume is varied, a phenomenon we name system-size observability resonance by analogy with other types of stochastic resonance. For the parameters of this study, the maximum in the observability occurs at volumes similar to those of bacterial cells or of eukaryotic organelles. [source]

Trans -splicing of organelle introns , a detour to continuous RNAs

BIOESSAYS, Issue 9 2009
Stephanie Glanz
Abstract In eukaryotes, RNA trans -splicing is an important RNA-processing form for the end-to-end ligation of primary transcripts that are derived from separately transcribed exons. So far, three different categories of RNA trans -splicing have been found in organisms as diverse as algae to man. Here, we review one of these categories: the trans -splicing of discontinuous group II introns, which occurs in chloroplasts and mitochondria of lower eukaryotes and plants. Trans -spliced exons can be predicted from DNA sequences derived from a large number of sequenced organelle genomes. Further molecular genetic analysis of mutants has unravelled proteins, some of which being part of high-molecular-weight complexes that promote the splicing process. Based on data derived from the alga Chlamydomonas reinhardtii, a model is provided which defines the composition of an organelle spliceosome. This will have a general relevance for understanding the function of RNA-processing machineries in eukaryotic organelles. [source]