Localization of two human homologs, HHR6A and HHR6B, of the yeast DNA repair gene RAD6 to chromosomes Xq24-q25 and 5q23-q31.

The chromosomal localizations of two closely related human DNA repair genes, HHR6A and HHR6B, were determined by in situ hybridization with biotinylated probes. HHR6A and HHR6B (human homolog of yeast RAD6) encode ubiquitin-conjugating enzymes (E2 enzymes), likely to be involved in postreplication repair and induced mutagenesis. The HHR6B gene was assigned to human chromosome 5q23-q31, whereas the HHR6A gene was localized on the human X chromosome (Xq24-q25). This latter assignment was confirmed with an X-specific human-mouse/hamster somatic cell hybrid panel. Southern blot analysis points to an X and an autosomal localization of HHR6A and HHR6B, respectively, in the mouse. The potential involvement of these genes in human genetic disorders is discussed.     

Localization and quantification of extracellular polymers in methanogenic granular sludge

Summary Extracellular polymers were localized and quantitatively analysed in methanogenic granular sludge cultivated on either propionate or ethanol in laboratory upflow anaerobic sludge-blanket (UASB) reactors. Electron microscopical analysis of ultrathin sections of the two sludge types stained with ruthenium red revealed the presence of extracellular polymers with different densities and structures. For quantification, granular sludge from a large-scale UASB reactor at a liquid sugar plant was also included in this study. A three-step physical disintegration procedure was used to extract water-soluble extracellular material from the granules. After each disintegration step the extracts were analysed for polysaccharides and proteins. Cell damage and thus the contribution of intracellular proteins and polysaccharides was estimated simultaneously by the determination of free DNA and free ATP in the extracts. After two extraction steps, up to 3.5 mg polysaccharides/g organic material and 5.5 mg protein/g organic material were extracted, whereas no significant increase in DNA was detected. The role of extracellular polymers in granular stability is discussed. Offsprint requests to: A. J. B. Zehnder     

Characterization of In Vivo Reporter Systems for Gene Expression and Biosensor Applications Based on luxAB Luciferase Genes

Advances in genetic engineering methods have allowed the development of an increasing number of practical and scientific applications for bioluminescence with lux genes cloned from a variety of organisms. Bioluminescence derived from the shortened lux operon (luxAB genes) is a complex process, and applications seem to be proliferating in advance of an understanding of the underlying biochemical processes. In this report, we describe a two-phase kinetic behavior of the light emission which must be properly taken into account in any quantitative measurements of the bioluminescence signal. By using strains of Escherichia coli and Caulobacter crescentus, this behavior was characterized and interpreted in terms of the biochemistry underlying the bacterial luciferase mechanism. We show that the intensity profile of each of the two phases of the luminescence signal is responsive (and exhibits different sensitivities) to the concentration of added decanal and other components of the assay mix, as well as to the order of mixing and incubation times. This study illustrates the importance of appropriate protocol design, and specific recommendations for using the luxAB system as a molecular reporter are presented, along with versatile assay protocols that yield meaningful and reproducible signals.     

Automated measurement of root length with a three-dimensional high-resolution scanner and image analysis

For measuring the length of root samples, the use of a three-dimensional (3D) scanner is proposed to address the problem of a too low resolution. The scanner's high resolution (up to 354 pixels per cm) enables in the resulting grey-value image very thin roots (diameter 100 m) to be segmented from the background by a simple thresholding operation. After skeletonizing, total length of the roots is calculated by multiplying the number of skeleton pixels by a correction factor. A comparison with the modified Newman Line-Intersect Method showed a correlation of r=0.98. Besides its superior resolution, an advantage of this type of scanner is its focusing depth, which allows root samples to be recorded on the scanbed similarly to a camera-oriented system.     

Vegetation Changes Following Large-scale Fence Removal Across a Protected Area Network Within the Kruger to Canyons Biosphere Reserve,South Africa

Ecosystems - In the early 1990’s, reserves adjacent to Kruger National Park (KNP) removed their fences to create a continuous landscape within the Kruger to Canyons Biosphere Reserve....