Markers for trans-Golgi Membranes and the Intermediate Compartment Localize to Induced Membranes with Distinct Replication Functions in Flavivirus-Infected Cells

Replication of the flavivirus Kunjin virus is associated with virus-induced membrane structures within the cytoplasm of infected cells; these membranes appear as packets of vesicles associated with the sites of viral RNA synthesis and as convoluted membranes (CM) and paracrystalline arrays (PC) containing the components of the virus-specified protease (E. G. Westaway, J. M. Mackenzie, M. T. Kenney, M. K. Jones, and A. A. Khromykh, J. Virol. 71:6650-6661, 1997). To determine the cellular origins of these membrane structures, we compared the immunolabelling patterns of several cell markers in relation to these sites by immunofluorescence and immunoelectron microscopy. A marker for the trans-Golgi membranes and the trans-Golgi network, 1,4-galactosyltransferase (GalT), was redistributed to large foci in the cytoplasm of Kunjin virus-infected cells, partially coincident with immunofluorescent foci associated with the putative sites of viral RNA synthesis. As determined by immunoelectron microscopy, the induced vesicle packets contained GalT, whereas the CM and PC contained a specific protein marker for the intermediate compartment (ERGIC53). A further indicator of the role of cellular organelles in their biogenesis was the observation that the Golgi apparatus-disrupting agent brefeldin A prevented further development of immunofluorescent foci of induced membranes if added before the end of the latent period but that once formed, these membrane foci were resistant to brefeldin A dispersion. Reticulum membranes emanating from the induced CM and PC were also labelled with the rough endoplasmic reticulum marker anti-protein disulfide isomerase and were obviously redistributed during infection. This is the first report identifying trans-Golgi membranes and the intermediate compartment as the apparent sources of the flavivirus-induced membranes involved in events of replication.     

Structural consequences of mutation.

The way a protein responds to mutation provides key insights into its architecture and energetics. Mutations are improving the understanding both of protein folding and stability, and of the adaptability of the hydrophobic core. The importance of intermolecular effects in crystal structures is being emphasized and new insights into the correspondence between crystal and solution structures are being developed.     

An implantable transducer for measuring tension in an anterior cruciate ligament graft.

The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a femoral fixation device. To devise a practical in vivo calibration protocol for the fixation device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.     

Pendelluft flow in symmetric airway bifurcations.

We propose a mathematical model for pendelluft flow in a single airway bifurcation. The model is motivated by an apparatus used in an experimental study of the pendelluft by Ultman et al. (1988). We derive differential equations governing the fluid flow, which directly connect physiological parameters to the variables determining the pendelluft; this approach allows us to include nonlinearity in the model. If nonlinearity is neglected, our model is identical to the R-I-C circuits used by previous investigators. If nonlinearity is retained, we show that pendelluft can occur even in perfectly symmetric airway bifurcations. For the specific apparatus used in the experiments of High et al. (1991), we demonstrate that two qualitatively different pendelluft flows can occur in the system.