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381.
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Chemical synapses are highly specialized cell–cell junctions designed for efficient signaling between nerve cells. Distinct
cytoskeletal matrices are assembled at either side of the synaptic junction. The presynaptic cytomatrix at the active zone
(CAZ) defines and organizes the site of neurotransmitter release from presynaptic nerve terminals. The postsynaptic density
(PSD) tethers neurotransmitter receptors and the postsynaptic signal transduction machinery. Recent progress in the identification
and characterization of novel CAZ and PSD components has revealed new insights into the molecular organization and assembly
mechanisms of the synaptic neurotransmission apparatus. On the presynaptic side, Bassoon and Piccolo, two related giant proteins,
are crucially involved in scaffolding the CAZ. On the postsynaptic side, two families of multi-domain adaptor proteins, the
MAGuKs (membrane-associated guanylate kinase homologs) and the ProSAP (proline-rich synapse-associated protein, also termed
Shank) family members are thought to be major organizing molecules of the PSD. 相似文献
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John S. Rinehart 《Die Naturwissenschaften》1976,63(5):218-223
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Hopanoids are pentacyclic triterpenoid lipids occurring in bacteria. They are synthesized from isopentenyl units which are
formed in a new biosynthetic route leading to isopentenyl diphosphate. Six C5 units are joined to form squalene, the immediate precursor in hopanoid synthesis. In a highly complex cyclization reaction
that shares considerable similarities with that of oxidosqualene to sterols, the hopane skeleton is formed from squalene by
the squalene-hopene cyclase. Recent elucidation of the X-ray structure of this membrane-bound cyclase has shed some light
on the properties of this unusual enzyme. The active site is located in a cavity within the enzyme. The squalene substrate
diffuses through a channel structure from the membrane into this cavity and is there transformed into hopene. Polar side chains
are attached to hopene resulting in the amphiphilic molecular structure of many hopanoids. These hopanoids are membrane components
involved in regulating membrane fluidity and stability. However, the many structural variants of hopanoids indicate that they
may have other interesting but as yet unknown functions. 相似文献
390.
In 1964, Walter Rothenbuhler proposed a two-gene model to explain phenotypic variance in the remarkable behavior in which honey bee workers remove dead brood from their colonies. Rothenbuhler's model proposed that one locus controls the uncapping of brood cells containing dead pupae, while a second controls the removal of the cell contents. We show here, through molecular techniques and quantitative trait loci (QTL) linkage mapping, that the genetic basis of hygienic behavior is more complex, and that many genes are likely to contribute to the behavior. In our cross, we detected seven suggestive QTLs associated with hygienic behavior. Each detected QTL controlled only 9-15% of the observed phenotypic variance in the character. 相似文献