Mutation of the conserved Gly94 and Gly126 in elongation factor Tu from Escherichia coli. Elucidation of their structural and functional roles

All guanine-nucleotide-binding proteins cycle between an inactive, GDP-bound and an active, GTP-bound conformation whereby they function as molecular switches. Elongation factor Tu from Escherichia coli is used as a model for defining residues important in the switch mechanism. Gly94 and Gly126 were separately mutated to alanine residues to study their role in the switch mechanism. The mutant proteins are denoted [G94A]EF-Tu and [G126A]EF-Tu, respectively. Both mutations affect the affinities for guanine nucleotides considerably, resulting in a decrease in the characteristic preference for GDP over GTP. Furthermore the [G94A]EF-Tu mutant possesses an increased GTPase activity. The aminoacyl-tRNA affinity is much reduced for [G94A]EF-Tu, as reflected in an increase of the dissociation rate constant for the ternary complex by a factor of 40. Surprisingly, however, both mutants in their GDP forms have a low, but significant affinity for aminoacyl-tRNA, which is not seen for the wild-type elongation factor Tu. The mutants only exhibit minor changes compared to the wild type with respect to in vitro translation of a poly(U) messenger.     

Controlling free flight of a robotic fly using an onboard vision sensor inspired by insect ocelli

Scaling a flying robot down to the size of a fly or bee requires advances in manufacturing, sensing and control, and will provide insights into mechanisms used by their biological counterparts. Controlled flight at this scale has previously required external cameras to provide the feedback to regulate the continuous corrective manoeuvres necessary to keep the unstable robot from tumbling. One stabilization mechanism used by flying insects may be to sense the horizon or Sun using the ocelli, a set of three light sensors distinct from the compound eyes. Here, we present an ocelli-inspired visual sensor and use it to stabilize a fly-sized robot. We propose a feedback controller that applies torque in proportion to the angular velocity of the source of light estimated by the ocelli. We demonstrate theoretically and empirically that this is sufficient to stabilize the robot''s upright orientation. This constitutes the first known use of onboard sensors at this scale. Dipteran flies use halteres to provide gyroscopic velocity feedback, but it is unknown how other insects such as honeybees stabilize flight without these sensory organs. Our results, using a vehicle of similar size and dynamics to the honeybee, suggest how the ocelli could serve this role.     

Impact of past and future residential housing development patterns on energy demand and related emissions

The continued outward growth from a central business district has been the dominant characteristic of most cities in Australia. However, this feature is seen as unsustainable and alternative scenarios to contain the outward growth are being proposed. Melbourne is currently grappling with this issue while simultaneously trying to reduce per capita greenhouse gas emissions. Housing size, style and its location are the three principal factors which determine the emissions from the residential sector. This paper describes a methodology to assess the combined impact of these factors on past and possible future forms of residential development in Melbourne. The analysis found that the location of the housing and its size are the dominant factors determining energy use and greenhouse gas emissions.     

Applications of Euclidean constructions to computer graphics

This paper presents an interactive graphics system called L.E.G.O. The purpose of L.E.G.O. is to model two- and three-dimensional objects using Euclidean geometry constructions. L.E.G.O. has a layered structure which makes it convenient to use, both for the experienced programmer and the novice. The programs may be written in a compiled language (C), written interactively in an interpreted language (LISP) or developed using a graphical interface in a multiple-window environment. Applications of L.E.G.O. include computer-assisted instruction of geometry and computer graphics, geometric modeling, and kinematic analysis. The use of imperative constructions and the powerful interface based on the idea of graphical programming are the most distinctive features of the system.     

Infection after total elbow arthroplasty

The purpose of this study was to review our experience with the treatment of twenty-five infections (in twenty-five patients) after total elbow arthroplasty and to examine indications for salvage of the prosthesis compared with those for resection arthroplasty. The patients were divided into three groups on the basis of treatment. Group I comprised fourteen patients who were managed with multiple, extensive irrigation and debridement procedures with retention of the original components. The primary indication for retention of the prosthesis was evidence that it was well fixed as determined both radiographically and intraoperatively. Group II comprised six patients who had removal of the prosthesis and debridement followed by immediate or staged reimplantation. Group III comprised five patients who were managed with resection arthroplasty. The infection was successfully eradicated in seven of the fourteen elbows that had salvage of the prosthesis with irrigation and debridement. The results were strongly dependent on the causative organism; attempts at debridement failed in the four elbows that were infected with Staphylococcus epidermidis compared with three of the ten that were infected with another organism. Four of the six patients in Group II had successful reimplantation of a prosthesis; in three, the infection had been caused by an organism other than Staphylococcus epidermidis. Only one of the three patients who had a Staphylococcus epidermidis infection had a successful reimplantation. None of the five patients who had a resection arthroplasty had signs of infection at the latest follow-up examination. We concluded that salvage of the prosthesis with extensive irrigation and debridement in the presence of an infection about the elbow can be reasonably successful if the infecting organism is not Staphylococcus epidermidis and if the components are well fixed. When removal of the components is warranted, staged reimplantation can also be highly successful when the infecting organism is not Staphylococcus epidermidis. However, the repeated operations necessary to retain a prosthesis and the high rates of complications seen with this approach--and the relatively good rates of satisfaction obtained with resection arthroplasty--suggest that resection arthroplasty remains the procedure of choice in medically frail patients or in patients for whom function of the elbow is less of a concern.     

Socioeconomic status and use of family planning among Ghanaian government workers

The low utilization of family planning methods in Ghana, and by inference in much of Africa, is explained by reference to traditional sociocultural values held by males. A LISREL model is tested using data collected from educated males working in the Ghanaian government. Among the findings are that lack of couple communication, segregated conjugal role relationships, and male-dominated decision-making are all significant predictors of non-use of family planning methods (pronatalist attitude is not). Possession of knowledge of family planning among Ghanaian males alone is unlikely to initiate use of family planning methods. Additional sociodemographic and modernization findings are reported.     

Does palpability of primary cutaneous melanoma predict dermal invasion?

BACKGROUND: Relatively few studies have addressed the question of whether clinical estimation of melanoma thickness by palpation can accurately predict its histologic thickness. If palpability was a reliable predictor of dermal invasion, it could be used to define the surgical margin. OBJECTIVE: We sought to determine whether clinical elevation of melanoma could be used to predict the presence or absence and the degree of dermal invasion in patients with stage 1 cutaneous melanoma. METHODS: Melanomas in 165 patients were categorized by one observer as flat, just palpable, palpable, or nodular. This was compared with histologic measurements of tumor thickness. RESULTS: Overall there was significant correlation between the degree of palpability of melanoma and the presence or absence of dermal invasion (p<0.001), Breslow thickness (p<0.0001), and Clark level (p<0.001). However, the relation between palpability and Breslow thickness for invasive melanomas less than 1 mm thick was weaker (n=62, p=0.053), and the correlation between elevation and Clark level was not significant for invasive melanomas less than 4 mm thick (n=111, p>0.999). CONCLUSION: We conclude that palpability of melanoma is an inadequate guide to the presence or absence and degree of dermal invasion in melanomas less than 1 mm thick and cannot be used to determine the surgical margin.     

Volatile anaesthetics reduce adhesion of blood platelets under low-flow conditions in the coronary system of isolated guinea pig hearts

BACKGROUND: Inhibitory effects of volatile anaesthetics on platelet aggregation have been demonstrated in several studies. However, the influence of volatile anaesthetics on intracoronary platelet adhesion has not been elucidated so far. METHODS: Isolated hearts of guinea pigs were perfused with buffer in the absence or presence of volatile anaesthetics (0.5 and 1 MAC) at constant coronary flow rates of 5 ml/min for 25 min, then 1 ml/min for 30 min and again 5 ml/min for 10 min. Before, during and after low-flow perfusion, a bolus of human platelets was applied into the coronary system. To simulate thrombogenic conditions, 0.3 U/ml human thrombin was infused during low-flow perfusion and reperfusion. The number of platelets sequestered to the endothelium was calculated from the difference between coronary in- and output of platelets. The myocardial production of lactate and consumption of pyruvate and coronary perfusion pressure were also determined. RESULTS: At a flow rate of 5 ml/min only about 3% of the applied platelets did not emerge from the coronary system, in any group. In contrast, 13.1 +/- 1.2% (mean +/- SEM) of infused platelets became adherent in low-flow perfusion in the control group without anaesthetic. The adherence was reduced with each 1 MAC isoflurane (to 6.2 +/- 1.2%), sevoflurane (to 4.4 +/- 0.9%) or halothane (to 3.2 +/- 1.5%) (each P < 0.05 vs. control). Volatile anaesthetic, 0.5 MAC, did not inhibit platelet adhesion to a statistically significant extent in any case. Perfusion pressure and metabolic parameters were not statistically different between the control and the hearts exposed to anaesthetics. CONCLUSION: Volatile anaesthetics in a concentration of 1 MAC can reduce the adhesion of platelets in the coronary system under reduced flow conditions. This action does not arise from vasodilation or inhibition of ischaemic stress.