A novel discrete mobile DNA element from Tn2l from the plasmid R100.1 is described, and its mobilization function was confirmed experimentally. In addition, the element behaves as a recombinase-active locus (tnpl) which facilitates insertions of antibiotic resistance genes as modules or cassettes at defined hot spots or integration sites. A similar tnpl sequence was detected by DNA hybridization in a series of P-lactamase transposons and plasmids and localized on their physical maps. The genetic function of the locus cloned from Tn2l into pACYC184 was tested for conduction and integration into the plasmids R388 and pOX38Km, and the results suggested recombinase-integrase activity and recA independence. DNA sequence analysis of the tnpl locus revealed no inverted or direct terminal repeats or transposition features of class I and class II transposons. The coding capacity revealed three putative open reading frames encoding 131, 134, and 337 amino acids. Orf3 encoded a putative polypeptide product of 337 amino acids that shared highly significant identity with the carboxyl region of integrase proteins. A comparison and an alignment of the tnpl locus from Tn2l and its flanking sequences identified similar sequences in plasmids and in transposons. The alignment revealed discrete nucleotide changes in these tnpl-like loci and a conserved 3' and 5' GTTA/G hot spot as a duplicated target site. Our data confirm the remarkable ubiquity of tnpl associated with antibiotic resistance genes. We present a model of transposon modular evolution into more complex multiresistant units via tnpl and site-specific insertions, deletions, and DNA rearrangements at this locus.Plasmid-mediated P-lactamases in gram-negative bacteria constitute a family of related but biochemically distinct enzymes, now numbering more than 40, that determine resistance to penicillins, cephalosporins, and other 1-lactam

This work presents the implementation of data-parallel perspective volume rendering on a massively parallel SIMD computer, the MasPar MP-1, and shows the benefits of e$icient indirect addressing (an MP-1 feature) which allows individual processing elements to address their local memory independently. Emphasis is put on the geometric transformations required for volume rendering algorithms. TJte data-parallel algorithm separates multi-dimensional spatial transformations into a series of one-dimensional operations that can be performed in parallel on regular data domains, providing performance linear with data size. The rotation andperspective transformation is reduced to four shearlscale passes. The separable approach allows for predictable and regular data handling, independent of data values, allowing optimization of communication between processing elements. The communications required are data axis transpositions, wJtich can be peflormed using the MP-1 's global router, which delivers scalable peflormance. Wrtualization allows graceful scaling in both problem size and architecture size, and a hierarchical design provides a flexible and portable fiamework suitable for different data-parallel SIMD architectures.1 IMAGE-BASED VISUALIZATION Massively data-parallel architectures can realise close to peak performance on regularly structured image processing and viewing operations, allowing in some cases for real-time (or near real-time) interaction with modelling and viewing parameters [17]. A number of special architectures have been used for volume rendering [ 111.Polygon-based graphic algorithms pose problems of scalability, discretization independent of problem domain, and dependence on special purpose hardware for high performance [9]. Image-or pixel-based algorithms can be scalable with problem size, need not introduce geometrical artifacts and can be implemented on general purpose data-parallel computers. As a result, increases in model complexity (e.g. molecular modelling), empirical data generated from sensors (e.g. remote sensing and medical imaging) and inter-* action impose requirements that polygon-based systems often cannot satisfy. Image-based approaches are particularly well-suited to handling large multidimensional empirical data and the integration of computer vision, computer graphics and image processing 131.2 DATA-PARALLEL VOLUME RENDERING The data-parallel algorithm achieves data access regularization by following the approach taken by Drebin&al.[4], which is a source for better efficiency in data access. Data-parallel geometrical transformations, including rotation and perspective, are applied to the data to localize projection rays within individual processing element memories. Once localization is completed, iso-surface rendering is computed using Levoy's technique [12]. This consists of computing voxel opacities for iso-surface classification, computing Phong shading, and compositing along the viewing rays for the final view (See also [21] for an extensive discussion on volume rendering iss...

A series of intragenic DNA probes, encoding the major part of the transposase resolvase and inverted repeats of transposons Tn3, Tn2l, and Tn25O1, were used in hybridization assays for homologous DNA sequences in 18 transposons studied. The tnpA and tnpR probes detected extensive homology with Tn3-like and Tn21-like elements for 11 transposons. This high degree of homology was confirmed with the 38-and 48-base-pair inverted-repeat oligonucleotide probes of Tn3, Tn2l, and Tn2S01. The Southern-type gel hybridization experiments localized the tnpA-homologous sequences on the physical DNA maps constructed. The genetic and physical maps of the transposons were compared, as were their nucleic acid sequence homologies. These comparisons suggested a subfamily of mobile elements distinct from but related to the Tn2l group. Based on these results, an evolutionary model is proposed and a pedigree is presented for the genesis of multiresistance ,-lactamase transposons.More than 30 biochemically distinct P-lactamases are known to be plasmid encoded in gram-negative bacteria (21,24,25,28).

Transposon Tn1403 is a 19.9-kb multiresistance class II transposable element originally found on the RPL11 plasmid from a clinical isolate of Pseudomonas aeruginosa. It encodes resistance to ampicillin (PSE-1 beta-lactamase), streptomycin and spectinomycin (aadA and aphC), and chloramphenicol (cat). It has structural homology with the tnpM and tnpI sequences of Tn21 and inverted repeats and res and tnpR sequences of Tn501, but it has no structural homology nor functional complementation with the resolvase gene of Tn21 or Tn3. Sequence analysis revealed long inverted repeats at each extremity of Tn1403 containing 38-bp inverted repeats that were 97.4% similar to those of Tn1721 and 5-bp direct repeats. Transposition assays showed a low frequency of transposition (3.5 x 10(-6)) compared with that of Tn3 (3.3 x 10(-3)) and no resolution of cointegrates.

The L-1 penicillinase structural gene, bWaS, from Pseudomonas maltophilia has been cloned into the vector pACYC184. The pMON01 recombinant plasmid selected by ampicillin resistance carried a 2.6-kilobase Sau3A fragment of P. maltophilia DNA and was confirmed to express L-1 P-lactamase by comparative isoelectric focusing. A detailed physical map was constructed, and the blaS structural gene was localized with a 17-mer oligonucleotide mixed probe encoding the L-1 N-terminal amino acid sequence. Induction studies confirmed constitutive expression. Isolation of a complete j8-lactamase operon was attempted by construction of a P. maltophilia genomic library into phage X 2001. A recombinant phage was selected by DNA hybridization, and the 13.4-kilobase DNA insert was physically mapped and subcloned into plasmid vectors. Expression and L-1 ,-lactamase synthesis were studied in Escherichia coli.