Microtubule mechanics and the implications for their assembly

Microtubules are cytoskeletal protein polymers relevant to a wide range of cell functions. In order to polymerize, the constituent tubulin subunits need to bind the nucleotide GTP, but its subsequent hydrolysis to GDP in the microtubule lattice induces depolymerization. The resulting behaviour of stochastic switching between growth and shrinkage is called dynamic instability. Both dynamic instability and microtubule mechanical properties are integral to many cell functions, yet are poorly understood. The present study uses thermal fluctuation measurements of grafted microtubules with different nucleotide contents to extract stiffnesses, relaxation times, and drag coefficients with an unprecedented precision. Both the stiffness and the relaxation time data indicate that stiffness is a function of length for GDP microtubules stabilized with the chemotherapy drug taxol. By contrast, measurements on microtubules polymerized with the non-hydrolizable GTP-analogue GMPCPP show a significantly higher, but constant, stiffness. The addition of taxol is shown to not significantly affect the properties of these microtubules, but a lowering of the GMPCPP content restores the length-dependent stiffness seen for taxol microtubules. The data are interpreted on the basis of a recent biopolymer model that takes into account the anisotropic architecture of microtubules which consist of loosely coupled protofilaments arranged in a tube. Using taxol microtubules and GMPCPP microtubules as the respective analogues of the GDP and GTP state of microtubules, evidence is presented that shear coupling between neighbouring protofilaments is at least two orders of magnitude stiffer in the GTP state than in the GDP state. Previous studies of nucleotide effects on tubulin have focussed on protofilament bending, and the present study is the first to be able to show a dramatic effect on interprotofilament bonds. The finding’s profound implications for dynamic instability are discussed. In addition, internal friction is found to dominate over hydrodynamic drag for microtubules shorter than ∼ 4 μm and, like stiffness, to be affected by the bound nucleotide, but not by taxol. Furthermore, the thermal shape fluctuations of free microtubules are imaged, and the intrinsic curvatures of microtubules are shown for the first time to follow a spectrum reminiscent of thermal bending. Regarding the extraction of mechanical data, this assay, though previously described in the literature, is shown to suffer from systematic flaws

AN EVALUATION OF THE IMPACT OF A LIFE SKILLS PROGRAMME IN THE WORKPLACE

Tschohl (2004:24) states that too much emphasis is placed on increasing knowledge (which is important), but that companies can get far better returns on training investments by putting more focus on people skills. Tschohl added that competence building through Life Skills education may be the single most effective preventative strategy for dealing with social issues and concerns in most communitie

THE APPROPRIATENESS AND NECESSITY OF SHORT-TERM THERAPY IN THE CONTEXT OF THE EMPLOYEE ASSISTANCE PROGRAMME

The existence of work-related problems such as job stress experienced by employees in the workplace and personal problems such as marital problems, interpersonal problems and emotional stress underlines the importance of psychotherapy by employee assistance professionals. Googins as quoted by Sprang (1992:57) emphasises the fact that there is a need for Employee Assistance Programme (EAP) service delivery to be cost effective in order to be beneficial to both employee and employer

Removal of zinc from a base-metal solution using ion exchange at Rustenburg Base Metal Refiners.

Includes abstract.Includes bibliographical references.Anglo American Platinum’s expansion project, which aimed at increasing platinum production to 3.5 million oz per annum, necessitated an expansion in the Rustenburg Base Metal Refinery (RBMR) to accommodate the associated increase in the production of base metals (Cu, Ni, and Co). RBMR’s name plate capacity increased from 21 000 to 33 000 tonnes of nickel per annum. The expansion project involved various brownfield and greenfield installations and was completed in 2011. The new circuit and various process additions posed a significant risk to the nickel cathode quality with regard to zinc contamination. Mass balancing of the pre-expansion circuit showed that as much as 50% of the zinc entering the plant would exit through the nickel cathode, thus making it the major bleed for zinc from the circuit. The expansion circuit mass balance showed that although a portion of the zinc would exit through the pressure iron removal residue, this small bleed stream would not be sufficient to ensure that the nickel cathode does not exceed 50 ppm (LME specification). Another factor contributing to the zinc problem was the fact that more Platreef ore, with higher zinc levels, was being mined. These factors indicated that a dedicated zinc removal section was required to ensure a sustainable nickel cathode production containing less than 50 ppm zinc

OCCUPATIONAL SOCIAL WORK AND EMPLOYEE ASSISTANCE PROGRAMMES: CONTRIBUTIONS FROM THE WORLD OF WORK

Since the inception of the first formal Employee Assistance Programme (EAP) in South Africain 1986 by the Chamber of Mines of South Africa, as a result of a feasibility study completed inDecember 1985, there has been enormous growth in this field of specialisation. Services weresoon expanded beyond the mining industry and infiltrated sectors such as the financial sector,food sector and motor industry, to name a few. The public sector soon followed, but it wasonly in 1996 that a formal commitment was made by the Department of Public ServiceAdministration (DPSA) to issue instructions to government departments on national, provincialand local authority level

A NEEDS ASSESSMENT FOR A MANAGEMENT TRAINING PROGRAMME FOR STAFF OFFICERS AND AREA MANAGERS IN THE SOUTH AFRICAN NATIONAL DEFENCE FORCE (SANDF) SOCIAL WORK DIRECTORATE

Management is a process that requires both art and skill to be efficient and effective in service rendering. The goal of the study was to explore the need for a management training programme for staff officers and area managers in the SANDF Social Work Directorate in order to make recommendations for the development of a management training programme.This exploratory study utilised qualitative and quantitative methodology. No sampling was done as the entire population was used for the study. The staff officers and area managers inthe nine provinces in South Africa, within the SANDF, Social Work Directorate, were used as the population in the study.  The study clearly indicates that a formal management training programme is critical within the SANDF Social Work Directorate.  It is recommended that a formal management training programme should be implemented within the SANDF Social Work Directorate to address the management needs identified in this empirical study. Various identified experts should be utilised in the provision of training

Organizational development : a supplement for the effective organization

Much can be said about the pros and cons of organizational development (OD) in today’s ever-expanding and constantly evolving world of dynamic organizations. It may be argued that OD has even more of a place in today’s technologically advanced world of change and economic competitiveness. This article will discuss how OD may enhance the effectiveness of an organization within an evolving world. It is intended to contextualize OD and the process thereof, different phases in the action research model, and the necessity of training and development in OD. It will conclude with the similarities between OD and Employee Assistance Programs.http://www.tandfonline.com/loi/wjwb20hb201

THE INFLUENCE OF FAMILY DYNAMICS ON THE PRODUCTIVITY OF WORKING MOTHERS IN A MOTOR COMPANY IN SOUTH AFRICA

Since the inception of a non-racial, non-sexist democracy in South Africa in 1994, it is notsurprising to find many mothers have entered various professional fields and occupations. “Theinflux of women into the workforce, the economic necessity of two-income families, theincrease in single-parent families, child care and elder care availability and affordability, andincreased time pressure have all contributed to work and family concerns” (Gebeke, 1993:1).Unfortunately many families and businesses have neglected to adapt to these changes. Thewomen-in-business debate, however, has changed because so much has changed socially overthe last 15 years (Bendeman, 2007). The increased pressure that employers place on employeesto meet the needs of their customers and run a profitable business needs to be addressed, asemployers, according to Blanchard (2000), need to put effective structures and systems in placefor people to want to perform

FACTORS THAT HINDER THE UTILISATION OF THE EMPLOYEE ASSISTANCE PROGRAMME IN THE DEPARTMENT OF LABOUR

In 1999 the Department of Public Service and Administration developed and implemented anEmployee Assistance Programme (EAP) within the public service. This reaffirmed thegovernment’s commitment to intensify the programme to fight, inter alia, HIV and AIDS, andto deal with the traumas of everyday life, experiences of discrimination, cultural alienation andstress. A change in the programme focus has clearly occurred, to a certain extent, in response tothe major transformation in South African governmental and non-governmental organisations.This change occurred as a result of the introduction of worker-related regulations such as theBasic Conditions of Employment Act 75 of 1997, the Labour Relations Act 66 of 1995, theEmployment Equity Act 58 of 1998 and the Unfair Discrimination Act 4 of 2000, and made itnecessary for the employer to investigate, assess and assist employees with problems relating tosubstance abuse or incapacity. These acts formed a solid basis for implementing the EAP.The Department of Labour (DOL) responded promptly to the implementation of the EAP in2001, yet the programme remains under-utilised and is seen both by management andemployees of the Department as a social responsibility programme rather than a sound businessstrategy

Microtubule dynamics depart from wormlike chain model

Thermal shape fluctuations of grafted microtubules were studied using high resolution particle tracking of attached fluorescent beads. First mode relaxation times were extracted from the mean square displacement in the transverse coordinate. For microtubules shorter than 10 um, the relaxation times were found to follow an L^2 dependence instead of L^4 as expected from the standard wormlike chain model. This length dependence is shown to result from a complex length dependence of the bending stiffness which can be understood as a result of the molecular architecture of microtubules. For microtubules shorter than 5 um, high drag coefficients indicate contributions from internal friction to the fluctuation dynamics.Comment: 4 pages, 4 figures. Updated content, added reference, corrected typo