Giant phages are of interest for biocontrol of pathogenic bacteria, however, there is limited knowledge about their biology. We study the Salmonella phage SPN3US to better understand virion structure and function. SPN3US has a contractile tail and a large T=27 icosahedral capsid that contains its 240-kb genome. Previous analyses showed the SPN3US virion is highly unusual because it contains >80 different proteins, a number that is highly unusual for a tailed phage. In addition, there is a mass (>40 MDa) of proteins ("ejection proteins") within the head that enter the Salmonella cell, possibly with roles in host takeover at the onset of infection. However, there is limited knowledge of the composition of the mature particle, the roles of individual proteins and how the SPN3US head and virion assemble. To address this gap in knowledge this research characterized both wild-type phage and a tailless mutant of SPN3US using high performance mass spectrometry to more accurately define the head proteome. These data confirm the high structural complexity of the SPN3US virion with it containing 92 different proteins. The head was found to contain 54 proteins, of which 9 were determined to have undergone proteolytic cleavage by a phage-encoded protease. All of these processed proteins were cleaved C-terminal to the sequence motif AXE, including the protease responsible for these cleavages. These data provide new insight into head maturation events during virion assembly and form a strong foundation for future studies on the roles of individual head proteins. Overall, these experiments illustrate that mass spectrometry is a powerful tool for defining the composition of highly complex viral particles, including the identification of post-translational modifications indicative of maturation events during viral assembly, and could be more broadly implemented in the field.

Library of Congress Subject Headings

Bacteriophages; Salmonella--Structure; Proteins--Analysis

Publication Date


Document Type


Student Type


Degree Name

Bioinformatics (MS)

Department, Program, or Center

Thomas H. Gosnell School of Life Sciences (COS)


Julia A. Thomas

Advisor/Committee Member

Michael V. Osier

Advisor/Committee Member

Gary R. Skuse


RIT – Main Campus

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