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Knowledge of the complete genomic DNA sequence of an organism allows a systematic approach to defining its genetic components. The genomic sequence provides access to the complete structures of all genes, including those without known function, their control elements, and, by inference, the proteins they encode, as well as all other biologically important sequences. Furthermore, the sequence is a rich and permanent source of information for the design of further biological studies of the organism and for the study of evolution through cross-species sequence comparison. The power of this approach has been amply demonstrated by the determination of the sequences of a number of microbial and model organisms. The next step is to obtain the complete sequence of the entire human genome. Here we report the sequence of the euchromatic part of human chromosome 22. The sequence obtained consists of 12 contiguous segments spanning 33.4 megabases, contains at least 545 genes and 134 pseudogenes, and provides the first view of the complex chromosomal landscapes that will be found in the rest of the genome.

Nutrient limitaton is a critical signal in Salmonela virulence gene regulation. The katF (rpoS) gene mediates the expression of the Salkionella spy p i virulence genes during bacterial starvation. A katF Salmonella mutant has Increased su bilit to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagnal environment of host macrophages. Moreover, the katF mutant has g ntly reduced virulence in mice. katF encodes an alternative a factor of RNA polymerase which coordinately regulates Sabnonela viruence.

A SalmoneUla gene encoding a cytolysin has been identified by screening for hemolysis on blood agar. DNA sequence analyses together with genetic mapping in Salmonella suggest that it is unrelated to other toxins or hemolysins. The gene (slyA) is present in every strain of Salmonella examined, in Shigela, and in enteroinvasive Escherichia coli but not in other Enterobacteriaceae. SlyA (salmolysin) purified from a derivative of the original clone has hemolytic and cytolytic activity and has a molecular weight predicted by the DNA sequence. The median lethal dose and infection kinetics in mice suggest that the toxin is required for virulence and facilitates SalmoneUa survival within mouse peritoneal macrophages.

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