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Two mutagenic events are required to make null mutations of polyhomeotic (ph), which suggests that the locus is complex. Amorphic mutations (ph degrees) die in mid-embryogenesis and completely lack ventral thoracic and abdominal epidermal derivatives, whereas single-event mutations lead to transformations similar to those of known dominant gain of function(More)
Thymosin beta 4 is acknowledged as a major G-actin binding protein maintaining a pool of unassembled actin in motile vertebrate cells. We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells. Tbeta 4 behaves as a simple G-actin sequestering(More)
Aqueous solutions of alcohol-acetic acid-formalin or glutaraldehyde-acrolein were shaken with heptane and heptane phase used for fixation. Phase-partition fixation is akin to fixation with vapor. The organic solvent, immiscible with water, penetrates hydrophobic membranes and carries the fixative in contact with water phase of the tissue. Only the fixative(More)
Semliki Forest virus enters cells by receptor-mediated endocytosis. The acidic environment of the endosome triggers a membrane fusion reaction that is mediated by the E1 glycoprotein. During fusion, E1 rearranges from an E1/E2 heterodimer to a highly stable, membrane-inserted E1 homotrimer (E1HT). In this study, we analyzed E1HT by a combination of electron(More)
Biological objects may be arrested in defined stages of their activity by fast freezing and may then be structurally examined. If the time between the start of activity and freezing is controlled, structural rearrangements due to biological function can be determined. Cryo-electron microscopy shows great potential for the study of such time-dependent(More)
Myosin subfragment-1-induced polymerization of G-actin into arrowhead-decorated F-actin-myosin subfragment-1 (S1) filaments has been studied at low ionic strength and in the absence of ATP, using a combination of light scattering, fluorescence of 4-nitrobenz-2-oxa-1,3-diazol-7-yl- or pyrenyl-labeled actin, sedimentation, and electron microscopy techniques.(More)
The segmented pattern of the Drosophila embryo depends on a regulatory cascade involving three main classes of genes. An early regulatory programme, set up before cellularization, involves direct transcriptional regulation mediated by gap and pair-rule genes. In a second phase occurring after cellularization, interactions between segment-polarity genes are(More)
Rotaviruses are important human pathogens with a triple-layered icosahedral capsid. The major capsid protein VP6 is shown here to self-assemble into spherical or helical particles mainly depending upon pH. Assembly is inhibited either by low pH (<3.0) or by a high concentration (>100 mM) of divalent cations (Ca(2+) and Zn(2+)). The structures of two types(More)
Rotavirus is a nonenveloped virus with a three-layered capsid. The inner layer, made of VP2, encloses the genomic RNA and two minor proteins, VP1 and VP3, with which it forms the viral core. Core assembly is coupled with RNA viral replication and takes place in definite cellular structures termed viroplasms. Replication and encapsidation mechanisms are(More)
The recent determination of the crystal structure of VP6, the major capsid protein of rotavirus, revealed a trimer containing a central zinc ion coordinated by histidine 153 from each of the three subunits. The role of the zinc ion in the functions of VP6 was investigated by site-directed mutagenesis. The mutation of histidine 153 into a serine (H153S and(More)