PubMed · 8791412
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V M Fowler, R Vale. 1996. Cytoskeleton.. https://doi.org/10.1016/s0955-0674(96)80040-8
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This review discusses molecular motors that use the microfilament and microtubule cytoskeletal systems in filamentous fungi. There has been an explosion in our knowledge of kinesins over the past year, because of the integration of genetic and biochemical data. The recognition of possible interactions between septation genes and cytokinesis has also advanced our understanding of microfilament-based cytoskeletal systems. We review recent findings on microfilament motors, including conventional and unconventional myosins, and the microtubule motors of the kinesin family and cytoplasmic dynein. The roles that these molecules play in hyphal morphogenesis and organelle transport provide an insight into cytoskeletal-based transport systems.
Mammalian ELAV proteins bind to polyadenylated messenger RNAs and have specificity for AU-rich sequences. Preferred binding sites in vitro include the AUUUA pentamer and related sequences present in the 3' untranslated regions of many growth regulatory mRNAs. Human ELAV (hELAV) proteins have been implicated in post-transcriptional regulation of gene expression by their effects on the stability and translatability of growth regulatory mRNAs. We have examined the intracellular localization of ELAV proteins in neurons and in tumor cells of neuronal origin using indirect immunofluorescence, confocal microscopy and biochemical separation. Mammalian neuronal ELAV proteins are found predominantly in the cytoplasm of cells in mRNP complexes termed alpha complexes which, when associated with polysomes, form large and high density ss complexes, as assayed by glycerol and accudenz gradients, respectively. Puromycin, cytochalasin or EDTA treatments disrupt beta complexes causing the release of alpha complexes, which then appear, by confocal microscopy, as large hELAV mRNP granules associated with microtubules. Association of partially purified hELAV mRNP alpha complexes with microtubules was confirmed by in vitro reconstitution assays. Furthermore, colchicine treatment of cells suggested that association of hELAV mRNP alpha complexes with microtubules is also necessary for the formation of ss complexes. Our data suggest a model in which a subset of mRNAs is associated with microtubules as ELAV mRNP particles (alpha complexes) which, in turn, associate with polysomes to form a translational apparatus (beta complex) that is, through polysomes, associated with the microfilament cytoskeletal network. hELAV proteins in these mRNP granules may affect post-transcriptional regulation of gene expression via the intracellular transport, localization and/or translation of growth regulatory mRNAs.
Budding and vesiculation of erythrocyte membranes occurs by a process involving an uncoupling of the membrane skeleton from the lipid bilayer. Vesicle formation provides an important means whereby protein sorting and trafficking can occur. To understand the mechanism of sorting at the molecular level, we have developed a micropipette technique to quantify the redistribution of fluorescently labeled erythrocyte membrane components during mechanically induced membrane deformation and vesiculation. Our previous studies indicated that the spectrin-based membrane skeleton deforms elastically, producing a constant density gradient during deformation. Our current studies showed that during vesiculation the skeleton did not fragment but rather retracted to the cell body, resulting in a vesicle completely depleted of skeleton. These local changes in skeletal density regulated the sorting of nonskeletal membrane components. Highly mobile membrane components, phosphatidylethanolamine- and glycosylphosphatidylinositol-linked CD59 with no specific skeletal association were enriched in the vesicle. In contrast, two components with known specific skeletal association, band 3 and glycophorin A, were differentially depleted in vesicles. Increasing the skeletal association of glycophorin A by liganding its extrafacial domain reduced the fraction partitioning to the vesicle. We conclude that this technique of bilayer/skeleton uncoupling provides a means with which to study protein sorting driven by changes in local skeletal density. Moreover, it is the interaction of particular membrane components with the spectrin-based skeleton that determines molecular partitioning during protein sorting.