Geospatial Semantics: Why, of What, and How?

Abstract. Why are notions like semantics and ontologies suddenly getting so much attention, within and outside geospatial information communities? The main reason lies in the componentization of Geographic Information Systems (GIS) into services, which are supposed to interoperate within and across these communities. Consequently, I look at geospatial semantics in the context of semantic interoperability. The paper clarifies the relevant notion of semantics and shows what parts of geospatial information need to receive semantic speci-fications in order to achieve interoperability. No attempt at a survey of ap-proaches to provide semantics is made, but a framework for solving interopera-bility problems is proposed in the form of semantic reference systems. Particular emphasis is put on the need and possible ways to ground geospatial semantics in physical processes and measurements. 1. Introduction: Wh

Rapidly labelled ribonucleoprotein particles in rat liver cytoplasm and their relevance to the transport of messenger RNA

The appearance of rapidly labelled particles in the cytoplasm of rat liver has been followed in animals treated with 0.5 mg/kg actinomycin D to inhibit the synthesis of ribosomal subunits. Particles labelled under these conditions show a polydisperse sedimentation pattern on sucrose gradients, extending from 10 to 80 S with a maximum at 30 S. On CsCl gradients their density is 1.54 g/cm3. A component with a density of 1.38 g/cm3 has been observed under certain conditions, but this is considered to be an artifact. The RNA found in these particles has a polydisperse distribution on sucrose gradients extending from 7 to 35 S with a maximum at 17 S. Rapidly labelled non-ribosomal RNA is transported to the cytoplasm and becomes associated with polysomes in the presence of both actinomycin D and cycloheximide during short labelling periods. These results are discussed in relation to theories of the transport of mRNA from the nucleus to the cytoplasm

MreB of Streptomyces coelicolor is not essential for vegetative growth but is required for the integrity of aerial hyphae and spores

MreB forms a cytoskeleton in many rod-shaped bacteria which is involved in cell shape determination and chromosome segregation. PCR-based and Southern analysis of various actinomycetes, supported by analysis of genome sequences, revealed mreB homologues only in genera that form an aerial mycelium and sporulate. We analysed MreB in one such organism, Streptomyces coelicolor. Ectopic overexpression of mreB impaired growth, and caused swellings and lysis of hyphae. A null mutant with apparently normal vegetative growth was generated. However, aerial hyphae of this mutant were swelling and lysing; spores doubled their volume and lost their characteristic resistance to stress conditions. Loss of cell wall consistency was observed in MreB-depleted spores by transmission electron microscopy. An MreB–EGFP fusion was constructed to localize MreB in the mycelium. No clearly localized signal was seen in vegetative mycelium. However, strong fluorescence was observed at the septa of sporulating aerial hyphae, then as bipolar foci in young spores, and finally in a ring- or shell-like pattern inside the spores. Immunogold electron microscopy using MreB-specific antibodies revealed that MreB is located immediately underneath the internal spore wall. Thus, MreB is not essential for vegetative growth of S. coelicolor, but exerts its function in the formation of environmentally stable spores, and appears to primarily influence the assembly of the spore cell wall