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Physical Review Letters

The presented approach describes a new strategy for creating product structures, which are suitable for further customer driven product customization – i.e. the customization can be carried out within less time and for lower costs. The required input data is knowledge on the interconnectivity between product components and knowledge of principal scopes of customization demands (e.g. which components or functions customers would like to individualize, which ones are unknown or hidden). By means of specific computer support, the designer can identify potentialities of customization at early design phases and derive useful measures of optimization. Because of the new strategy, designers obtain detailed propositions for structure related design adaptations supporting the aptitude for customizing the concerned product later on. If the direct customer interaction takes place (i.e. if a specific customization demand is on hand), the product adaptation can be carried out promptly - and due to the optimized structure with less invest.

Modulation of gene expression via nucleic acid sequence-specific intervention represents a new paradigm for drug discovery and development. Ribozymes are small RNA structures capable of cleaving RNA target molecules in a catalytic fashion. A 2'-O-allyl-modified hammerhead ribozyme designed to cleave the messenger RNA of cytochrome P-450 3A2 was administered to rats via 0.25 mg intravenous injections to investigate the disposition of this compound. The chemically modified ribozyme binds to serum albumin and can be displaced by phosphorothioate oligonucleotides. A biphasic plasma clearance with a distribution half-life of 12 min and an elimination half-life of 6.5 h was observed. A volume of distribution of 2.1 l/kg indicates perfusion into tissues well beyond the vascular system. The chemically modified ribozyme can be detected intact in the plasma up to 48 h after injection. Metabolic degradation of the chemically modified ribozyme occurs at unmodified ribonucleotides, leaving the 2'-O-allyl-modified sites intact. Recovery of intact chemically modified ribozyme was 1.9% of the administered dose at 12 h along with significant metabolites. The renal clearance of the intact ribozyme is an average 34.3 ml/h. The tissue distribution of the chemically modified ribozyme at 48 h is primarily to kidney and liver but the only detected material is a single 27-mer metabolite that has been cut in the unmodified GAAA region. The brain concentration of the prominent 27-mer metabolite is greater than that observed in the lung or spleen. Examination of tissues reveals no morphological evidence of toxicity. These data strongly support the potential utility of synthetic, 2'-O-allyl-modified hammerhead ribozymes as therapeutic agents in vivo.

In the upcoming years, significant changes in the profile of satellite missions are expected as scientists and managers want to benefit from multi-satellite missions. Among others, distributed or virtual satellite platforms will create a completely new class of space missions, where not one single spacecraft or payload segment has to be operated but a formation or constellation of satellites. A “formation” designates multiple satellites in close proximity and is typically characterized by demanding guidance, navigation and control requirements. In comparison to perform these tasks by a ground control approach, on-board autonomy can guarantee superior performance with respect to control accuracies and cost efficiency. A dedicated research and development program on “Autonomous Spacecraft Navigation and Formation Flying” was initiated at DLR/GSOC in 1998. Numerous contributions in the area of space-borne GPS receiver technology, precision relative navigation and autonomous orbit control of satellite formations as a prerequisite for spacecraft autonomy have been made. Practical experience in the operations of a two-satellite formation has been gained by the GRACE mission. Next, GSOC is supporting Swedish Space Cooperation (SSC) in the implementation of the PRISMA formation flying demonstration mission, where a fully autonomous, robust and precise formation flying of spacecraft will be conducted by experiment. Finally, the German TerraSAR-X/TanDEM-X radar satellites will be Europe’s first space mission equipped and operated routinely with an autonomous formation flying system.

Low-redundancy automated DNA sequencing by primer walking is described. T7 DNA polymerase is used together with computer-selected walking primers and fluorescein-dATP as internal label to sequence large plasmids or cosmids directly on a standard DNA sequencer with an error rate below 1% up to 500 bases (in the unedited raw data). The low error rate allows efficient sequencing with low (2-3 times) redundancy. Plasmid subclones covering 20 kb of a cosmid insert were sequenced with an overall redundancy of 2.7 in the course of the European community Saccharomyces cerevisiae genome sequencing project. Neighboring plasmid subclones were linked by direct cosmid sequencing. Sets of ten walking primers are synthesized on the EMBL multiple segmental DNA synthesizer at low costs and used for sequencing with greater than 95% efficiency. The accuracy of the directed approach is improved by simultaneous walking on both strands by designing two primers in opposite directions in the same starting region. One primer is used to confirm sequence data on the opposite strand, and the other primer to obtain new sequence data.

We have identified additional criteria for the walking primer design that improve the success rate of automated fluorescent DNA sequencing using the internal labeling technique and T7 DNA polymerase. These criteria resulted from the evaluation of over 220 sequences generated with walking primers and fluorescein-15-dATP as internal label in the course of the European Community (EC) yeast genome sequencing project. In this project primers were designed using standard commercial software. Intensities of sequencing signals varied over a broad range from very strong to very weak, depending on the primers used. This led us to evaluate primer performance relative to (i) the template sequence immediately downstream of the primer binding site and (ii) the primer sequence itself. Our experiments show that the position of the first labeled dATP to be incorporated downstream of the primer into the growing strand is substantial for the signal intensity of the sequence. The closer to the primer that the first 'A' is incorporated, the stronger the peak intensities are. An additional feature of sequencing with native T7 DNA polymerase is its ability to remove a 3'-terminal 'A' of the primer by the 3'--5' exonuclease activity and to exchange the nucleotide with a labeled dATP by the polymerase activity.