In many dsDNA viruses, a single-strand-annealing homologous recombination (SSA) reaction is catalyzed by a pair of proteins. In phage lambda, this system is called Red, and is composed of lambda exonuclease (Lambda-Exo, a 5' to 3' dsDNA exonuclease), and Red-Beta (a ssDNA binding protein and annealase). I examined the physical and mechanistic coupling of Lambda-Exo and Red-Beta and confirmed that these proteins form a complex with a 1:1 subunit stoichiometry. The size of this complex was shown to be close to one MDa, possibly composed of 12 Lambda-Exo and 12 Red-Beta monomers. Red-Beta decreased the extent of digestion of dsDNA by Lambda-Exo, possibly by preventing its rebinding. The processivity of Lambda-Exo was not affected by Red-Beta, but the dwell-time of Lambda-Exo was significantly increased by Red-Beta. These effects of Red-Beta on Lambda-Exo may have important roles in controlling the SSA reaction by preventing hyper-resection of DNA, and/or by stabilizing Lambda-Exo/DNA complexes. The previous observations that Red-Beta protects ssDNA from nucleases and that SSB inhibits Red-Beta assembly onto ssDNA were confirmed and strengthened by our results. We determined that Red-Beta inhibits SSB binding to nascent ssDNA generated by Lambda-Exo. This strongly suggests that generation of nascent ssDNA by Lambda-Exo is coupled to assembly of Red-Beta onto nascent ssDNA. We describe two models for this coupled assembly: Model One suggests that Lambda-Exo loads Red-Beta on nascent ssDNA providing a kinetic advantage over SSB, and Model Two proposes that the complex of Lambda-Exo and Red-Beta feeds ssDNA directly onto the dodecameric Red-Beta ring. It was suggested that Lambda-Exo forms a topological link with nascent ssDNA, thereby making digestion highly processive. We challenged this model by removing the nascent ssDNA with ExoI during a Lambda-Exo digestion reaction. We observed that the nascent ssDNA was a major contributor to the processivity of Lambda-Exo since removal of nascent ssDNA resulted in a drastic decrease in the processivity of Lambda-Exo. This is the first demonstration that DNA is a processivity factor, strengthening the view that processive DNA processing enzymes should be thought of as nucleoprotein complexes that must be kinetically treated as both substrate and enzyme.

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A biomechanical model of the glenohumeral joint has been developed to investigate muscle and joint loading during real life three-dimensional activities. Based on a rigid body mechanics approach, the model incorporates algorithms to correct for curved muscle paths and bone geometry, providing realistic muscle orientation over a wide range of limb positions. An optimization routine has been incorporated, minimizing overall maximum muscle stress in the 26 individual muscle elements considered. The model utilizes anatomical muscle and bone data, subject anthropometric data, kinematics measured using a 6 camera Vicon motion analysis system and hand loading measured using a force-plate and mobile six-component strain gauged force transducer developed for this project. Model stability and sensitivity to input data uncertainties have been investigated. Data used for this was actual subject activity data. Random uncertainties of a known statistical distribution were generated using a Monte Carlo data perturbation technique and superimposed on the subject data. No model instability or unacceptable error magnification was demonstrated in this investigation. A study of real life three-dimensional activities has been conducted using five male subjects. Normalized, averaged muscle and joint forces were calculated for each activity. Using the same five subjects, electromyographic (EMG) muscle activation was measured for the same five activities. Both surface and intra-muscular fine wire electrode techniques were used. Eight muscles including infraspinatus, subscapularis and supraspinatus were instrumented. The resulting EMG data was normalized and averaged for each activity. Muscle activation appears in good agreement with published EMG and our own EMG study. Overall joint compressive and shear forces of up to 7 and 2 times body weight respectively have been calculated. Results of the study indicate glenohumeral joint forces for athletic activities can be as high as 7 times those forces previously predicted in other studies for simple abduction and flexion.

Abstract Background: It is well documented in the international literature that when implants have been placed with primary stability in the edentulous mandible, immediate or early loading of the implants can be highly successful. Success rates of between 85-98% have been reported.1 However, no evidence has been published on the success rates of implants placed post-extraction with immediate or early loading in South Africa. Objectives: The investigation reported in this dissertation was undertaken to compare the success rates of early loaded implants placed in a) Edentulous mandibles and maxillae (delayed placement), b) “Fresh” extraction sockets with prior alveolectomies within the mandible/maxilla (immediate placement). Methods: In a private maxillo-facial surgical practice and a private prosthodontic practice, the number of patients who had received implants, number of implants per patient, type of implant placed (Southern or Nobel Biocare), total number of implants, site of implant placement and type of prosthesis placed were recorded. The success rates were evaluated using the following criteria3: A) Absence of clinically detectable implant mobility B) Absence of soft tissue infections, persistent pain, paraesthesia, or discomfortimplants, site of implant placement and type of prosthesis placed were recorded. The success rates were evaluated using the following criteria3: A) Absence of clinically detectable implant mobility B) Absence of soft tissue infections, persistent pain, paraesthesia, or discomfortimplants, site of implant placement and type of prosthesis placed were recorded. The success rates were evaluated using the following criteria3: A) Absence of clinically detectable implant mobility B) Absence of soft tissue infections, persistent pain, paraesthesia, or discomfortC) Radiographic evaluation of bone loss D) Period of follow-up, that is loading period Results: The records of 22 patients who had had 121 implants placed with early loading over a 3 - 45 month period were studied. Of the 121 implants, 107 implants showed no bone loss, and 14 showed bone loss. Furthermore, 4 implants were lost in 2 patients, both patients having had implants placed in edentulous jaws. No clinical complications were seen in any patients. Conclusions: Implants with early loading placed in edentulous jaws showed a 94.1% survival rate during the study period, while those placed into fresh and immediately post-extraction sockets showed a 100% survival rate. The failure rate was too low for further analysis.