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Abstract
Methicillin resistant Staphylococcus aureus (MRSA) is a global public health concern. The mobile genetic element responsible for the transition from methicillin sensitive to methicillin resistant S. aureus is Staphylococcal Cassette Chromosome mec or SCCmec. Little is known about the mechanisms employed by SCC elements to be maintained within the bacteria and mobilize to new cells. While SCC elements carry a variety of virulence factors as accessory proteins, to further understand how SCC elements are maintained and transferred, I have focused on the conserved proteins of SCC elements. The goal of this work has been to gain a better understanding of the functions of the SCC element conserved proteins. By understanding the function of these conserved proteins, we can then extrapolate how they may be utilized in maintenance and transfer. Each SCC element encodes 7 conserved proteins grouped into 3 adjacent operons. The first operon of SCC elements contains proteins with functions related to DNA replication. I developed a plasmid - based assay to test whether or not these proteins could facilitate extrachromosomal DNA replication. Although they did not, the optimized assay will be useful in the study of other mobile genetic elements. The second operon encodes the site-specific recombinases that facilitate excision and integration into the chromosome. Lastly little was known about the 3rd conserved operon except that one of the encoded proteins, SaUGI, inhibits uracil DNA glycosylase. I showed that SaUGI has additional activities: overexpression of it led to a decrease in biofilm production, cell wall defects, and many changes in gene expression. Additionally, I identified Ccg as a uracil DNA glycosylase. Finally, I discuss potential roles for the conserved proteins in the horizontal transfer and how they fit within a new model of transfer via natural competence.