from PART III - Paradigms of Bacterial Evolution
Published online by Cambridge University Press: 16 September 2009
INTRODUCTION
Like most eubacteria, S. aureus possesses a variety of mobile genetic elements (MGEs) that contribute in major ways to pathogenesis and its evolution. In addition to the typical MGEs carried by most bacteria, that is, prophages, transposons, and plasmids, S. aureus possesses two types of novel elements that have not been described for other bacteria, namely the superantigen-encoding pathogenicity islands and the resistance-encoding SCCmec elements. In this chapter, the general properties of these various MGEs are summarized, with special emphasis on the two novel types and on their contributions to pathogenesis and its evolution.
MOLECULAR GENETICS OF THE STAPHYLOCOCCAL MGEs
Plasmids
For a comprehensive review of plasmid origins and interactions, see Firth and Skurray (2006). Staphylococcal plasmids range in size from 1.2 to more than 100 kb; all known staphylococcal plasmids are circular duplex DNA, using either of the two standard modes of replication, theta and rolling circle (RC), with the latter being used principally by those of less than 10 kb, and the former by those larger, though this is only an approximate dividing line. As with all other plasmids, replication of staphylococcal plasmids is negatively autoregulated. For the known small RC plasmids, this is accomplished by cis-encoded antisense RNAs, sometimes with the assistance of small proteins. Theta plasmids of the pSK41/pGO1 family also appear to use an antisense mechanism.
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