that the pathogenicity island contains the genes to regulate genes located outside of the pathogenecity island. Additionally, regulatory genes outside of the PAI may regulate virulence genes in the pathogenicity island. Regulation genes typically encoded on PAIs include AraC-like proteins and two-component response regulators. PAIs can be considered unstable DNA regions as they are susceptible to deletions or mobilization. This may be due to the structure of PAIs, with direct repeats, insertion sequences and association with tRNA that enables deletion and mobilization at higher frequencies. Additionally, deletions of pathogenicity islands inserted in the genome can result in disrupting tRNA and subsequently affect the metabolism of the cell. Examples The P fimbriae island contains virulence factors such as haemolysin, pili, cytotoxic necrosing factor, and uropathogenic specific protein (USP). Yersinia pestis high pathogenicity island I has genes regulating iron uptake and storage. Salmonella SP1 and SP2 sites. Rhodococcus equi virulence plasmid pathogenicity island encodes virulence factors for proliferation in macrophages. The SaPI family of Staphylococcus aureus pathogenicity islands, mobile genetic elements, encode superantigens, including the gene for toxic shock syndrome toxin, and are mobilized at high frequencies by specific bacteriophages. Phage encoded Cholera toxin of Vibrio cholerae, Diphtheria toxin of Corynebacterium diphtheriae, Neurotoxins of Clostridium botulinum and Cytotoxin of Pseudomonas aeruginosa. Helicobacter pylori has two strains, one being more virulent than the other due to the presence of the Cag pathogenicity island. References External links BAC definition of pathogenicity Genetics