The Xenopus oocyte is known to accumulate filamentous or F‐actin in the nucleus, but it is currently unknown whether F‐actin also accumulates in embryo nuclei. Using fluorescence‐labeled actin ...reporters, we examined the actin distribution in Xenopus embryonic cells and found that F‐actin accumulates in nuclei during the blastula stage but not during the gastrula stage. To further investigate nuclear F‐actin, we devised a Xenopus egg extract that reproduces the formation of nuclei in which F‐actin accumulates. Using this extract, we found that F‐actin accumulates primarily at the subnuclear membranous region and is essential to maintain chromatin binding to the nuclear envelope in well‐developed nuclei. We also provide evidence that nuclear F‐actin increases the structural stability of nuclei and contributes to chromosome alignment on the mitotic spindle at the following M phase. These results suggest the physiological importance of nuclear F‐actin accumulation in rapidly dividing large Xenopus blastula cells.
While nuclear F‐actin accumulates in Xenopus oocytes, it is unknown whether it does so in embryos. Using fluorescence‐labeled actin reporters and Xenopus egg extracts, we demonstrate that F‐actin accumulates in blastula nuclei, promoting chromatin–nuclear envelope binding, nuclear structural stability and M‐phase mitotic chromosome alignment.
Proteins and ribonucleoproteins containing a nuclear export signal (NES) assemble with the exportin Xpo1p (yeast CRM1) and Gsp1p-GTP (yeast Ran-GTP) in the nucleus and exit through the nuclear pore ...complex. In the cytoplasm, Yrb1p (yeast RanBP1) displaces NES from Xpo1p. Efficient export of NES-cargoes requires Yrb2p (yeast RanBP3), a primarily nuclear protein containing nucleoporin-like phenylalanine-glycine (FG) repeats and a low-affinity Gsp1p-binding domain (RanBD). Here, we show that Yrb2p strikingly accelerates the association of Gsp1p-GTP and NES to Xpo1p. We have solved the crystal structure of the Xpo1p-Yrb2p-Gsp1p-GTP complex, a key assembly intermediate that can bind cargo rapidly. Although the NES-binding cleft of Xpo1p is closed in this intermediate, our data suggest that preloading of Gsp1p-GTP onto Xpo1p by Yrb2p, conformational flexibility of Xpo1p, and the low affinity of RanBD enable active displacement of Yrb2p RanBD by NES to occur effectively. The structure also reveals the major binding sites for FG repeats on Xpo1p.
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•Yrb2p increases the association rate of Gsp1p-GTP and NES with Xpo1p•The crystal structure of Xpo1p-Yrb2p-Gsp1p-GTP complex is determined•Yrb2p primes Xpo1p and Gsp1p for rapid loading of NES by an allosteric mechanism•The structure also reveals the major FG-repeat binding sites on Xpo1p
Koyama et al. now look at how the Ran-binding protein Yrb2p (yeast RanBP3) promotes nuclear export of proteins and ribonucleoproteins. Yrb2p strikingly increases the rate of cargo loading onto the nuclear export receptor Xpo1p (yeast CRM1) through an allosteric mechanism.
Xpo1p (yeast CRM1) is the major nuclear export receptor that carries a plethora of proteins and ribonucleoproteins from the nucleus to cytoplasm. The passage of the Xpo1p nuclear export complex ...through nuclear pore complexes (NPCs) is facilitated by interactions with nucleoporins (Nups) containing extensive repeats of phenylalanine–glycine (so‐called FG repeats), although the precise role of each Nup in the nuclear export reaction remains incompletely understood. Here we report structural and biochemical characterization of the interactions between the Xpo1p nuclear export complex and the FG repeats of Nup42p, a nucleoporin localized at the cytoplasmic face of yeast NPCs and has characteristic SxFG/PxFG sequence repeat motif. The crystal structure of Xpo1p‐PKI‐Nup42p‐Gsp1p‐GTP complex identified three binding sites for the SxFG/PxFG repeats on HEAT repeats 14–20 of Xpo1p. Mutational analyses of Nup42p showed that the conserved serines and prolines in the SxFG/PxFG repeats contribute to Xpo1p‐Nup42p binding. Our structural and biochemical data suggest that SxFG/PxFG‐Nups such as Nup42p and Nup159p at the cytoplasmic face of NPCs provide high‐affinity docking sites for the Xpo1p nuclear export complex in the terminal stage of NPC passage and that subsequent disassembly of the nuclear export complex facilitates recycling of free Xpo1p back to the nucleus.
This article describes structural and biochemical characterization of the interactions between the Xpo1p nuclear export complex and the FG repeats of Nup42p, a nucleoporin localized at the cytoplasmic face of nuclear pore complexes in yeast. The results of this study extend our understanding of the role of Nup42p in the terminal stage of nuclear export. The structure presented here also provides insights into evolutionary conservation of the FG repeat binding sites on CRM1 (Xpo1p) across species.
Xpo1p (yeast
CRM
1) is the major nuclear export receptor that carries a plethora of proteins and ribonucleoproteins from the nucleus to cytoplasm. The passage of the Xpo1p nuclear export complex ...through nuclear pore complexes (
NPC
s) is facilitated by interactions with nucleoporins (Nups) containing extensive repeats of phenylalanine–glycine (so‐called
FG
repeats), although the precise role of each Nup in the nuclear export reaction remains incompletely understood. Here we report structural and biochemical characterization of the interactions between the Xpo1p nuclear export complex and the
FG
repeats of Nup42p, a nucleoporin localized at the cytoplasmic face of yeast
NPC
s and has characteristic Sx
FG
/Px
FG
sequence repeat motif. The crystal structure of Xpo1p‐
PKI
‐Nup42p‐Gsp1p‐
GTP
complex identified three binding sites for the Sx
FG
/Px
FG
repeats on
HEAT
repeats 14–20 of Xpo1p. Mutational analyses of Nup42p showed that the conserved serines and prolines in the Sx
FG
/Px
FG
repeats contribute to Xpo1p‐Nup42p binding. Our structural and biochemical data suggest that Sx
FG
/Px
FG
‐Nups such as Nup42p and Nup159p at the cytoplasmic face of
NPC
s provide high‐affinity docking sites for the Xpo1p nuclear export complex in the terminal stage of
NPC
passage and that subsequent disassembly of the nuclear export complex facilitates recycling of free Xpo1p back to the nucleus.
There are many types of fibers come from creatures. However, in today’s high school biology, there is no complex educational program to learn fibers. Therefore, in this study, we developed an inquiry ...experimental system using natural fibers and practiced this program. First, as a plant fiber, we started growing cotton and as an animal fiber, used cocoon silk as teaching materials. Then, we also developed an experimental system using dry cocoons (spider, GFP) of non-living transgenic silkworms. With this system we succeeded in extracting DNA from the pupas about one year and determined whether they include recombinant DNA by PCR. By measuring the tensile strength of the fiber from each cocoon, we confirmed that the silk fiber from the spider cocoon was tough. In addition, by comparing the reactions of the silk fibers from each cocoon and cotton to each reagent, I made the students realize the differences among them as a substance. In this way, through these experiments of natural fibers we can integrate various studies, such as botany, entomology, biotechnology and clothing materials engineering. We can definitely say that the experimental system will make the students have different kinds of interests.
Ramie fabrics are often used for apparel, especially summer clothing. They have many interesting characteristics, such as durable properties for heavy use and cool contact feelings. In this study, we ...focused on the improvement of hard handling and poor resiliency of ramie fabrics. We modified ramie fabrics by light TEMPO oxidation and examined the effect of the oxidation on their texture. By TEMPO oxidation, a few carboxyl groups may be introduced to thesurfaceoframiefibers.Thedegree of introduction was about one seventh of the case of the preparation of cellulose nanofibers by TEMPO oxidation1 . TEMPO oxidation of ramie fabrics gave low bending stiffness and good drape properties, and as the result, ramie fabrics showed softer handlings and better flexibility.
To investigate the effect of delignification of ramie fabrics, we studied the effects of sodium chlorite treatment. The texture and physical properties of the treated ramie fabrics were evaluated ...using the Kawabata Evaluation System. We also investigated the surface structure, the wrinkle resistance, the water absorbency, the hygroscopic property, and the drying property. The physical properties including strength of the ramie fabrics were maintained after delignification. On the other hand, the water absorbency and the moisture content of ramie fabrics increased. This may be attributed to the higher hydrophilic nature of the surface of the treated fabrics. The air permeability obviously increased after delignification. The surface structure of the treated fabrics showed that each single yarn of the ramie fabrics became thinner and the fabrics became more porous after delignification. By delignification, ramie fabrics became more suitable for summer clothing.
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