Studies on the plasmid stability, plasmid copy number and endo(1, 3)(1, 4) b-glucanase production by free and alginate immobilised recombinant saccharomyces cerevisiae cells

A recombinant yeast strain, Saccharomyces cerevisiae DBY746, containing the plasmid pJG317, was grown in a variety of fermentation modes including batch, serial batch and chemostat culture incorporating a wide range of media types Plasmid pJG317 consists of a 2^-denved yeast episomal plasmid containing the gene which encodes for the bacterial enzyme endo (1,3)(1,4) P-glucanase. The concentration of enzyme produced appears to be proportional to the number of plasmid copies per cell. Specific enzyme activities were found to be in the range of 14 x 106 to 48 x lO6 U/cell for free cell culture, with a corresponding plasmid copy number of 8±0 5 to 40±6 3 copies per cell respectively. A procedure for measuring the copy number of pJG317 in S cerevisiae was developed, tested and optimised. The procedure is based on Southern hybridisation and measured the relative intensities of hybridisation of a probe to the single copy yeast chromosomal actin gene and to the multicopy plasmid pJG317. Plasmid pJG317 is quite unstable under non-selective conditions and its copy number and stability are influenced by both growth rate and nutrient supply By immobilising cells in calcium alginate gel beads, the plasmid could be stabilised and high volumetric productivities of up to 38 U/ml-h attained. Although radial gradients in biomass concentration and in percentage of plasmidcontaimng cells in the alginate gel beads were confirmed, no significant difference was found between the plasmid copy number of cells in the centre of the gel beads (36 5±6 8) and cells close to the surface of the gel beads(32 4± 33)

Malaria in Northern Ireland

The clinical features, parasitology and prophylactic history of 67 patients who imported malaria to Northern Ireland between 1974 and 1983 are reported. P. falciparum infections were encountered more frequently than anticipated from current United Kingdom experience. The clinical implications of these findings are discussed

The Nature of Reading Instruction in a Literature-based Reading Program

The purpose of this study was to describe the nature of reading instruction in a program using children's trade books instead of basal readers, and to identify patterns resulting in hypotheses regarding the nature of instruction. The study informs practitioners by providing descriptions of actual instruction, enabling readers to envision how reading instruction is accomplished using children's trade books, and it informs the research community by developing grounded theory concerning the nature of instruction in one literature-based reading program. The study can help bridge the polarization between traditionalists and whole language advocates through the descriptions of how traditionally accepted academic domains of reading instruction were accomplished. Also, it provides a model of a successful way to structure instructional time so that students spend more time actually reading, and it documents the social dimensions of instruction as important domain of reading instruction

Proceedings of the Near-Earth-Object Interception Workshop

The National Aeronautics and Space Administration Headquarters sponsored the Near-Earth-Object Interception Workshop hosted by the Los Alamos National Laboratory on 14-16 Jan. 1992 at the J. Robert Oppenheimer Study Center in Los Alamos, New Mexico. The Workshop evaluated the issues involved in intercepting celestial objects that could hit the Earth. It covered the technologies for acquiring, tracking, and homing, as well as those for sending interceptors to inspect, rendezvous with, land on, irradiate, deflect, or destroy them. This report records the presentations and technical options reviewed

The potential for biological control on cryptic plant invasions

Cryptic invasions can be defined as ‘the occurrence of an invasive species or genotype that was not previously recognised as alien in origin or not distinguished from other aliens’. Such invasions can result in negative impacts on the recipient ecosystems and disturb the evolutionary history of native plant populations. Many cryptic invasions have become so problematic that there is a need to implement control measures. This paper explores the potential for biological control to be implemented as a means of managing cryptic invasions. Firstly, the paper defines the different forms of cryptic invasion, differentiating between interspecific and intraspecific invasions; this hierarchy influences how to detect, study and ultimately implement biological control when cryptic invasions occur. Secondly, unique challenges associated with biological control programmes for cryptic invasions are addressed, including: the need for intraspecific level host specificity in agents, the occurrence of hybridisation between native species/lineages and the target weed, the role of enemy release in cryptic invasions in the presence of closely related native plant species/lineages, and a review of potential stakeholder conflicts of interest and legislation. Biological control of cryptic invasions has been shown to be possible, however the process will be more difficult and complex than controlling traditional targets and will likely take up more time and resources. If these challenges are overcome, then biological control programmes against cryptic invasions should be able to proceed and maintain the same standards as traditional biological control programmes

Cryogenic System for the Origins Space Telescope: Cooling a Large Space Telescope to 4K with Today's Technology

The Origins Space Telescope (OST) concept is one of four NASA Science Mission Directorate, Astrophysics Division, observatory concepts being studied for launch in the mid 2030's. OST's wavelength coverage will be from the midinfrared to the sub-millimeter, 6-600 microns. To enable observations at the zodiacal background limit the telescope must be cooled to about 4 K. Combined with the telescope size (currently the primary is 9 m in diameter) this appears to be a daunting task. However, simple calculations and thermal modeling have shown the cooling power required is met with several currently developed cryocoolers. Further, the telescope thermal architecture is greatly simplified, allowing simpler models, more thermal margin, and higher confidence in the final performance values than previous cold observatories. We will describe design principles to simplify modeling and verification. We will argue that the OST architecture and design principles lower its integration and test time and reduce its ultimate cost