TY - JOUR AB - Nuclear pore complexes (NPCs) are large multiprotein assemblies that allow traffic between the cytoplasm and the nucleus. During mitosis in higher eukaryotes, the Nuclear Envelope (NE) breaks down and NPCs disassemble. How NPCs reassemble and incorporate into the NE upon mitotic exit is poorly understood. We demonstrate a function for the conserved Nup107-160 complex in this process. Partial in vivo depletion of Nup133 or Nup107 via RNAi in HeLa cells resulted in reduced levels of multiple nucleoporins and decreased NPC density in the NE. Immunodepletion of the entire Nup107-160 complex from in vitro nuclear assembly reactions produced nuclei with a continuous NE but no NPCs. This phenotype was reversible only if Nup107-160 complex was readded before closed NE formation. Depletion also prevented association of FG-repeat nucleoporins with chromatin. We propose a stepwise model in which postmitotic NPC assembly initiates on chromatin via early recruitment of the Nup107-160 complex. AU - Walther, Tobias C. AU - Alves, Annabelle AU - Pickersgill, Helen AU - Loı̈odice, Isabelle AU - HETZER, Martin W AU - Galy, Vincent AU - Hülsmann, Bastian B. AU - Köcher, Thomas AU - Wilm, Matthias AU - Allen, Terry AU - Mattaj, Iain W. AU - Doye, Valérie ID - 11122 IS - 2 JF - Cell KW - General Biochemistry KW - Genetics and Molecular Biology SN - 0092-8674 TI - The conserved Nup107-160 complex is critical for nuclear pore complex assembly VL - 113 ER - TY - JOUR AB - In metazoa, the nuclear envelope breaks down and reforms during each cell cycle. Nuclear pore complexes (NPCs), which serve as channels for transport between the nucleus and cytoplasm1, assemble into the reforming nuclear envelope in a sequential process involving association of a subset of NPC proteins, nucleoporins, with chromatin followed by the formation of a closed nuclear envelope fenestrated by NPCs2,3,4,5,6,7. How chromatin recruitment of nucleoporins and NPC assembly are regulated is unknown. Here we demonstrate that RanGTP production is required to dissociate nucleoporins Nup107, Nup153 and Nup358 from Importin β, to target them to chromatin and to induce association between separate NPC subcomplexes. Additionally, either an excess of RanGTP or removal of Importin β induces formation of NPC-containing membrane structures—annulate lamellae—both in vitro in the absence of chromatin and in vivo. Annulate lamellae formation is strongly and specifically inhibited by an excess of Importin β. The data demonstrate that RanGTP triggers distinct steps of NPC assembly, and suggest a mechanism for the spatial restriction of NPC assembly to the surface of chromatin. AU - Walther, Tobias C. AU - Askjaer, Peter AU - Gentzel, Marc AU - Habermann, Anja AU - Griffiths, Gareth AU - Wilm, Matthias AU - Mattaj, Iain W. AU - HETZER, Martin W ID - 11121 IS - 6949 JF - Nature KW - Multidisciplinary SN - 0028-0836 TI - RanGTP mediates nuclear pore complex assembly VL - 424 ER - TY - JOUR AB - This paper studies the multicast routing and admission control problem on unit-capacity tree and mesh topologies in the throughput model. The problem is a generalization of the edge-disjoint paths problem and is NP-hard both on trees and meshes. We study both the offline and the online version of the problem: In the offline setting, we give the first constant-factor approximation algorithm for trees, and an -factor approximation algorithm for meshes. In the online setting, we give the first polylogarithmic competitive online algorithm for tree and mesh topologies. No polylogarithmic-competitive algorithm is possible on general network topologies (Lower bounds for on-line graph problems with application to on-line circuits and optical routing, in: Proceedings of the 28th ACM Symposium on Theory of Computing, 1996, pp. 531–540) and there exists a polylogarithmic lower bound on the competitive ratio of any online algorithm on tree topologies (Making commitments in the face of uncertainity: how to pick a winner almost every time, in: Proceedings of the 28th Annual ACM Symposium on Theory of Computing, 1996, pp. 519–530). We prove the same lower bound for meshes. AU - Henzinger, Monika H AU - Leonardi, Stefano ID - 11766 IS - 3 JF - Journal of Computer and System Sciences SN - 0022-0000 TI - Scheduling multicasts on unit-capacity trees and meshes VL - 66 ER - TY - JOUR AB - In this paper we consider the online ftp problem. The goal is to service a sequence of file transfer requests given bandwidth constraints of the underlying communication network. The main result of the paper is a technique that leads to algorithms that optimize several natural metrics, such as max-stretch, total flow time, max flow time, and total completion time. In particular, we show how to achieve optimum total flow time and optimum max-stretch if we increase the capacity of the underlying network by a logarithmic factor. We show that the resource augmentation is necessary by proving polynomial lower bounds on the max-stretch and total flow time for the case where online and offline algorithms are using same-capacity edges. Moreover, we also give polylogarithmic lower bounds on the resource augmentation factor necessary in order to keep the total flow time and max-stretch within a constant factor of optimum. AU - Goel, Ashish AU - Henzinger, Monika H AU - Plotkin, Serge AU - Tardos, Eva ID - 11764 IS - 2 JF - Journal of Algorithms SN - 0196-6774 TI - Scheduling data transfers in a network and the set scheduling problem VL - 48 ER - TY - CONF AB - This paper addresses the problem of topic distillation on the World Wide Web, namely, given a typical user query to find quality documents related to the query topic. Connectivity analysis has been shown to be useful in identifying high quality pages within a topic specific graph of hyperlinked documents. The essence of our approach is to augment a previous connectivity analysis based algorithm with content analysis. We identify three problems with the existing approach and devise algorithms to tackle them. The results of a user evaluation are reported that show an improvement of precision at 10 documents by at least 45% over pure connectivity analysis. AU - Bharat, Krishna AU - Henzinger, Monika H ID - 11897 SN - 01635840 T2 - 21st annual international ACM SIGIR conference on Research and development in information retrieval TI - Improved algorithms for topic distillation in a hyperlinked environment ER -