Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

Gail Christie


Staphylococcus aureus is one of the leading causes of nosocomial and community acquired infections. Many of the virulence factors are encoded on staphylococcal mobile genetic elements. Members of the SaPI family of S. aureus mobile elements encode superantigens and are mobilized at high frequency by specific helper bacteriophages. One remarkable feature of helper phage exploitation by SaPIs is remodeling of the normal T=7 bacteriophage capsid to produce smaller T=4 phage-like particles. These particles, composed entirely of helper phage proteins, can accommodate the smaller SaPI genome while excluding that of a complete helper phage. This study was designed to understand the mechanism of capsid size redirection and high frequency mobilization of SaPIs. A multipronged approach employing cryo-EM analysis, protein profile comparison and genetic analysis was used to study the capsid size redirection. Two proteins encoded by the prototype element SaPI1, gp6 and gp7, have been identified in SaPI1 procapsids but not in mature SaPI1 particles. These proteins are sufficient and required to direct small capsid formation, which involves alteration of an internal scaffold. While many phages use internal scaffolding proteins, the involvement of an internal scaffold in capsid size redirection is novel.


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Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2011