Kinetochores distinguish GTP from GDP forms of the microtubule lattice

During prometaphase in mitotic cell division, chromosomes attach to the walls of microtubules and subsequently move to microtubule ends, where they stay throughout mitosis. This end-attachment seems to be essential for correct chromosome segregating. However, the mechanism by which kinetochores, the multiprotein complexes that link chromosomes to the microtubules of the mitotic spindle, recognize and stay attached to microtubule ends is not understood. One clue comes from the hydrolysis of GTP that occurs during microtubule polymerization. Although tubulin dimers must contain GTP to polymerize, this GTP is rapidly hydrolysed following the addition of dimers to a growing polymer. This creates a microtubule consisting largely of GDP-tubulin, with a small cap of GTP-tubulin at the end. It is possible that kinetochores distinguish the different structural states of a GTP- versus a GDP-microtubule lattice. We have examined this question in vitro using reconstituted kinetochores from the yeast Saccharomyces cerevisiae. We found that kinetochores in vitro bind preferentially to GTP- rather than GDP-microtubules, and to the plus-end preferentially over the lattice. Our results could explain how kinetochores stay at microtubule ends and thus segregate chromosomes correctly during mitosis in vivo. This result demonstrates that proteins exist that can distinguish the GTP conformation of the microtubule lattice.     

XeF laser performance for F2and NF3fuels

XeF laser performance has been investigated for F2versus NF3as the halogen donor (fuel). The experiments were all performed in 3 AMAGAT Ne/Xe/fuel mixtures at ambient temperature and a pump rate of 132 KW/cm³on a 1 me-beam pumped laser. The F2-based laser mixture has been shown to be recyclable, with no loss in laser output, while laser performance steadily degrades for NF2-fueled mixtures under repetitively pulsed conditions. Despite the fact that F3absorbs at the XeF wavelength, it has been demonstrated that under appropriately chosen conditions the XeF intrinsic efficiency is essentially the same (2.2 percent) for both F2and NF3fuels for deposited energy loadings up to at least 150 j/l. Absorption, gain, fuel burn-up, and fluorescence were also measured in order to better characterize the laser medium and to determine the major factors contributing to the efficiency.     

Medical-resource use for suspected tuberculosis in a New York City hospital

OBJECTIVE: To compare resource use by diagnostic outcome among hospital admissions during which tuberculosis (TB) was suspected. DESIGN: Retrospective study based on chart review and microbiology laboratory data. SETTING: The department of medicine in a municipal hospital serving central Brooklyn, New York. PARTICIPANTS: We identified all adult admissions in 1993 during which TB was suspected. We assigned each admission to one of four mutually exclusive groups defined by the results of microbiological tests (acid-fast bacilli [AFB] smear and culture): culture-positive and smear-positive (C+S+); culture-positive and smear-negative (C+S-); culture-negative and smear-positive (C-S+); or culture-negative and smear-negative (C-S-). Each admission was divided into two separate periods to which the utilization of medical resources was assigned: the diagnostic and the postdiagnostic periods, which were separated by the date of receipt of the first definitive culture report. RESULTS: Data on 519 admissions (93 C+S+; 57 C+S-; 30 C-S+; and 339 C-S-) were analyzed. Although C+S+ were more likely than other groups to have an admitting diagnosis of TB, approximately one quarter of the admissions without TB (C-S+, C-S-) were admitted with the principal diagnosis of TB. For the four groups, C+S+, C+S-, C-S+, and C-S-, the respective rates of TB isolation and anti-TB treatment, and median lengths of isolation were 98%, 87%, and 34 days; 74%, 74%, and 7 days; 83%, 83%, and 15 days; and 44%, 29%, and 0 days. During the diagnostic period, the rate and length of isolation were similar in the AFB-smear-positive groups (C+S+ and C-S+). We estimated that admissions without culture-proven TB (C-S+ and C-S-) accounted for 3,174 (36%) of the 8,712 days of TB isolation expended and for 65% of the 16,671 days of anti-TB treatment. The vast majority of this resource consumption (2,737 [86%] of 3,174 days of isolation) occurred during the diagnostic period before a definitive culture result was known. CONCLUSIONS: Our results suggest that prolonged diagnostic uncertainty and misclassification of cases due to false-positive and false-negative smears are associated with substantial medical-resource consumption. New diagnostic modalities that reduce the period of diagnostic uncertainty could reduce the utilization of resources later found to be unnecessary.     

Effect of Dye Content on Point of Zero Charge of Anionic Lake Dyes

The pure dye content of FD&C yellow lake #5 and FD&C red lake #40 was found to be inversely related to the point of zero charge. The effect of the adsorbed anionic dye on the zeta potential of aqueous suspensions of FD&C yellow lake #5 at pH 5 was demonstrated.     

A separation principle between scheduling and admission control forbroadband switching

A framework for joint scheduling and admission control in broadband switching systems based on a principle of separation between these two levels of control is developed. It is shown that an admission control strategy can be tailored to a particular mix of traffic by using high-level information from the scheduler. This principle is presented in the context of asynchronous time-sharing (ATS) in which explicit guarantees of cell-level and call-level quality of service (QOS) are given to several traffic classes. The separation principle allows the formulation of an optimal admission control policy that maximizes the expected system utility and maintains all QOS guarantees. Several heuristic admission control policies are considered and compared with the optimal policy. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time traffic are used to illustrate the effects of different scheduling and admission control policies on both the expected utility and the admissable load region     

Mitotic chromatin regulates phosphorylation of Stathmin/Op18

Meiotic and mitotic spindles are required for the even segregation of duplicated chromosomes to the two daughter cells. The mechanism of spindle assembly is not fully understood, but two have been proposed that are not mutually exclusive. The 'search and capture' model suggests that dynamic microtubules become progressively captured and stabilized by the kinetochores on chromosomes, leading to spindle assembly. The 'local stabilization' model proposes that chromosomes change the state of the cytoplasm around them, making it more favourable to microtubule polymerization. It has been shown that Stathmin/Op18 inhibits microtubule polymerization in vitro by interaction with tubulin, and that overexpression in tissue culture cells of non-phosphorylatable mutants of Stathmin/Op18 prevents the assembly of mitotic spindles. We have used Xenopus egg extracts and magnetic chromatin beads to show that mitotic chromatin induces phosphorylation of Stathmin/Op18. We have also shown that Stathmin/Op18 is one of the factors regulated by mitotic chromatin that governs preferential microtubule growth around chromosomes during spindle assembly.     

Mitochondrial DNA variable number tandem repeats (VNTRs): utility and problems in molecular ecology

Analysis of mitochondrial (mt)DNA size polymorphism in the form of variable number tandem repeats (mtVNTRs) has become an increasingly popular methodology for addressing questions in molecular ecology. When detected by PCR, mtVNTR analysis can provide a sensitive, rapid, and cost-effective measure of genetic variability that may be exploited in studies of population differentiation and biogeography. Despite the emergence of this approach, there has been little critical evaluation of its success or utility as a practical tool. In this review, we identify problematic methodological, theoretical and interpretive factors that can influence the utility of mtVNTR analysis. The reliability of the procedure is considered in terms of both detection of alleles and scoring of intra-individual allele frequencies. While many of the potential technical problems of the technique do not raise serious practical concerns, this rapid and sensitive methodology is seriously compromised by the difficulty of reliably assessing allele frequencies, of assaying only germline tissue, and in our ignorance of the mechanisms generating mtVNTR diversity. Thus, although there is a considerable potential for mtVNTR pilot studies to assess genetic diversity, the utility of the technique to resolve broader questions in molecular ecology should be treated cautiously until such a time as the system is better understood.     

Association of apolipoprotein E epsilon2 and vasculopathy in cerebral amyloid angiopathy

Endogenous opioid peptides appear to be involved in acute behavioral effects induced by single doses of ethanol. However, its role in repeated ethanol exposure has not been studied. In the present study ethanol was given to rats at the doses of 2 and 4 g/kg by a stomach gauge for 15 days, and its effects on spontaneous motility, open-field activity, and active avoidance behavior recorded on the 3rd, the 6th and the 15th days. Then the effect of naloxone (0.5 and 2 mg/kg by intraperitoneal route) was tested against a challenge ethanol dose, administrated by oral route, on the 16th day. Control animals received tap water and saline instead of ethanol or naloxone, respectively. Both doses of ethanol induced a decrease in spontaneous motility that was antagonized by naloxone. Open-field ambulations were increased by the high dose of ethanol, low-dose lacking effect; naloxone did not modify these ethanol effects. The low dose of ethanol shortened latency time in shuttlebox, the high dose causing escape and freezing responses; none of these effects were modified by naloxone. Therefore, endogenous opioid peptides appear to play a limited role in the chronic effects of ethanol in rats; particularly its effects in tests inducing an increase in the level of anxiety were resistant to naloxone.