this diversity is located in discrete gene clusters that are spread throughout the different genomes. In contrast to this diversity, these enteric microorganisms exhibit marked synteny in their largescale genomic organization, bearing in mind that E. coli and S. enterica diverged about 100 Myr ago 28. The conserved genes may be a re¯ection of the basic lifestyle of the bacteria, requiring intestine colonization, environmental survival and transmission. The unique gene clusters probably contribute to adaptation to environmental niches and to pathogenicity. The pseudogene complement of S. typhi has implications for our understanding of the tight host restriction of this organism, and raises the question of whether it may be possible to eradicate S. typhi and typhoid fever altogether. M Methods Salmonella typhi CT18 was isolated in December 1993, at the Mekong Delta region of Vietnam, from a 9-year-old girl who was suffering from typhoid. The strain was isolated from blood using routine culture methods 23 , and after serological and metabolic con-®rmation of the strain as S. typhi it was immediately frozen in glycerol at-70 8C. The genome sequence was obtained from 97,000 end sequences (giving 7.9´coverage) derived from several pUC18 genomic shotgun libraries (with insert sizes ranging from 1.4 to 4.0 kb) using dye terminator chemistry on ABI377 automated sequencers. This was supplemented with 0.7´sequence coverage from M13mp18 libraries with similar insert sizes. End sequences from a larger insert plasmid (pSP64; 1.9´clone coverage, 10±14-kb insert size) and lambda (lambda-FIX-II; 0.4´clone coverage, 20±22-kb insert size) libraries were used as a scaffold, and the ®nal assembly was veri®ed by comparison with restriction-enzyme digest patterns using pulsed-®eld gel electrophoresis (data not shown). Total sequence coverage was 9.1´. The sequence was assembled, ®nished and annotated as described 29 , using Artemis 30 to collate data and facilitate annotation. In addition we used a gene®nder that was trained speci®cally for S. typhi, which uses a hidden Markov model with modules for the coding region, start and stop codons, and the ribosome-binding site (T.S.L. and A.K., unpublished data). The genome and proteome sequences of S. typhi and S. typhimurium or E. coli were compared in parallel to identify deletions and insertions using the Artemis Comparison Tool (ACT) (K. Rutherford, unpublished data; see also http://www.sanger.ac.uk/Software/ ACT/). Pseudogenes had one or more mutations that would ablate expression, and were identi®ed by direct comparison with S. typhimurium; each of the inactivating mutations was subsequently checked against the original sequencing data.

Human chromosome 7 has historically received prominent attention in the human genetics community, primarily related to the search for the cystic fibrosis gene and the frequent cytogenetic changes associated with various forms of cancer. Here we present more than 153 million base pairs representing 99.4% of the euchromatic sequence of chromosome 7, the first metacentric chromosome completed so far. The sequence has excellent concordance with previously established physical and genetic maps, and it exhibits an unusual amount of segmentally duplicated sequence (8.2%), with marked differences between the two arms. Our initial analyses have identified 1,150 protein-coding genes, 605 of which have been confirmed by complementary DNA sequences, and an additional 941 pseudogenes. Of genes confirmed by transcript sequences, some are polymorphic for mutations that disrupt the reading frame.

There is a significant demand for devices that can rapidly detect chemical–biological–explosive (CBE) threats on-site and allow for immediate responders to mitigate spread, risk, and loss. The key to an effective reconnaissance mission is a unified detection technology that analyzes potential threats in real time. In addition to reviewing the current state of the art in the field, this review illustrates the practicality of colorimetric arrays composed of sensors that change colors in the presence of analytes. This review also describes an outlook toward future technologies, and describes how they could possibly be used in areas such as war zones to detect and identify hazardous substances.

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The anionic nickel(II) porphyrin NiTPPS is able to selectively sense the spermine induced left-handed Z-form of DNA while it is completely silent in the presence of right-handed B-DNA. Interactions between the DNA and the porphyrin can be easily modulated by pH and temperature. The resulting Z-DNA-porphyrin-spermine complex behaves as a supramolecular reversible information storage system and as a reversible AND logic gate.