Active transport of proteins into the nucleus is mediated by interaction between the classical nuclear localization signals (NLSs) of the targeted proteins and the NLS receptor (importin) complex. This nuclear transport system is highly regulated and conserved in eukaryotes and is essential for cell survival. Using a fragment of BRCA1 containing the two NLS motifs as a bait for yeast two-hybrid screening, we have isolated four clones, one of which is importin ␣. Here we characterize one of the other clones identified, BRAP2, which is a novel gene and expressed as a 2-kilobase mRNA in human mammary epithelial cells and some but not all tissues of mice. The isolated full-length cDNA encodes a novel protein containing 600 amino acid residues with pI 6.04. Characteristic motifs of C2H2 zinc fingers and leucine heptad repeats are present in the middle and C-terminal regions of the protein, respectively. BRAP2 also shares significant homology with a hypothetical protein from yeast Saccharomyces cerevisiae, especially in the zinc finger region. Antibodies prepared against the C-terminal region of BRAP2 fused to glutathione S-transferase specifically recognize a cellular protein with a molecular size of 68 kDa, consistent with the size of the in vitro translated protein. Cellular BRAP2 is mainly cytoplasmic and binds to the NLS motifs of BRCA1 with similar specificity to that of importin ␣ in both two-hybrid assays in yeast and glutathione S-transferase pull-down assays in vitro. Other motifs such as the SV40 large T antigen NLS motif and the bipartite NLS motif found in mitosin are also recognized by BRAP2. Similarly, the yeast homolog of BRAP2 also binds to these NLS motifs in vitro. These results imply that BRAP2 may function as a cytoplasmic retention protein and play a role in regulating transport of nuclear proteins.The passage of macromolecules between the nucleus and the cytoplasm occurs through nuclear pores. Small macromolecules can diffuse through the nuclear pores at a rate inversely proportional to their mass. Proteins with molecular masses greater than 40 -60 kDa are actively transported through the nuclear pores. To be transported into the nucleus, the protein must either contain a nuclear localization signal or, if not, be bound to another protein that does (1, 2). This process requires at least four different factors acting in two distinct steps. The first step is mediated by importin ␣ (also termed karyopherin ␣) and importin  (also termed karyopherin ). The ␣ subunit is primarily responsible for NLS 1 recognition, whereas the  subunit appears to mediate docking to the nuclear pore complex. The second translocation step requires the small G protein Ran/TC4 and an interacting partner, p15 (3-13).The presence of a nuclear localization signal may not be sufficient to direct nuclear import. The target efficiency of NLS motifs can be modified by the presence of multiple NLS motifs within a protein, by modifications of the flanking sequences, and by the accessibility of the NLSs to the import machinery (1...
SUMMARYIEEE 802.11n could improve the network efficiency of WLAN by aggregating multiple frames into a single transmission. The frame aggregation technique especially benefits multi-hop transmissions that introduce enormous 802.11 medium access control (MAC) layer control overhead. This paper proposes a novel algorithm, namely dynamic aggregation selection and scheduling (DASS) algorithm, that can dynamically adopt the appropriate aggregation mechanism for IEEE 802.11s mesh network. The characteristics, benefits and the restrictions of three aggregation mechanisms, aggregate MAC service data units, aggregate MAC protocol data unit and aggregate physical protocol data unit, are investigated. Based on the channel condition, the quantity and the distribution of the frame arrivals, DASS could determine what aggregation mechanism to adopt and whether to wait for the next frame for aggregating transmissions. Simulation results demonstrate that the algorithm significantly increases the channel efficiency of the 802.11 MAC and further improves the overall throughput of the wireless mesh network by approximately 95%.
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