DESCRIPTION (provided by applicant): Streptococcus pyogenes (group A streptococcus, GAS) causes various infections of humans including the skin, throat, deep tissue, and even the bloodstream. Although these sites are rich in peptides and proteins, free amino acids, which are essential for this polyauxotrophic organism, are not abundant. The molecular details of the adaptive response to such natural environments are incompletely explored. This response needs to be understood, therefore, at the level of a regulatory network that links basic metabolic processes to virulence gene expression and enables the organism in a dynamic way to take advantage of protein-rich host environments. Based on the advances made in the genomics of GAS in recent years, this study proposes to (i) determine the breadth of the amino acid starvation response of GAS on a genome-wide scale, by global transcription profiling using DNA microarray technology. This approach will allow description of the amino acid starvation response of stringent (RelA+) and relaxed strains (RelA-) in laboratory media as well as in conditions that mimic or constitute in-vivo situations at a comprehensive level. To link the stringent response to the activity of CodY, a pleiotropic transcriptional repressor that senses the nutritional state of the cell, this study proposes to (ii) identify the target genes of CodY and their transcription pattern as a function of the relA-determined guanosine polyphosphate level. While this approach will enable the response to nutritional stress to be understood at the level of transcriptional regulation of the responsive genes, the third aim of this study proposes to (iii) determine global mRNA degradation patterns at the sub-genic, genic and operonic levels and explore molecular mechanisms involved in the alteration of mRNA half-lives. This will provide information about how transcript stability is influenced by environmental conditions. Taken together, this research should result in a comprehensive network of adaptive responses to a key environmental condition that GAS may encounter in association with their host. This knowledge will help understand pathogenetic mechanisms and may even lead to new approaches for treatment or prevention of streptococcal infections.