Microbiology

King successfully defends PhD thesis

King and Yahr

Jessica King successfully defended her PhD thesis, "Defining the Interaction of ExsA And LcrF with Type III Secretion System Gene Promoters," on Thursday, November 21, 2013. King is pictured here with her mentor, Timothy Yahr, PhD.

Transcription of the Pseudomonas aeruginosa type III secretion system is controlled by ExsA, a member of the AraC/XylS family of regulators. Each ExsA-dependent promoter contains two adjacent binding sites for monomeric ExsA. Binding site 1 consists of highly conserved GnC and TGnnA sequences that are individually recognized by the two helix-turn-helix (HTH) DNA-binding motifs of an ExsA monomer. I show that the two ExsA monomers bind to promoter regions in a head-to-tail orientation and identified residues in the first HTH of ExsA that contact the GnC sequence, and residues in the second HTH motif that contribute to the recognition of the TGnnA sequence. I also found that site 2 in the PexsC promoter region contains a GnC sequence that is functionally equivalent to the GnC in site 1 and recognized by the first HTH motif of an ExsA monomer while the second HTH interacts with an adenine residue in binding site 2. Hybrid promoter experiments indicate that ExsA-binding affinity, promoter strength, and the degree of promoter bending are determined by binding site 2.
 
During the ExsA studies I observed that the amino acids that comprise the HTH motifs of ExsA are nearly identical to those in LcrF/VirF, the activators of T3SS gene expression in the pathogenic yersiniae. I determined that Yersinia pestis LcrF binds to and activates transcription of ExsA-dependent promoters in P. aeruginosa, and that plasmid expressed ExsA complements a Y. pestis lcrF mutant for T3SS gene expression. Mutations that disrupt the ExsA consensus-binding sites in both P. aeruginosa and Y. pestis T3SS promoters prevent activation by ExsA and LcrF. All of the data combined demonstrate that ExsA and LcrF recognize a common nucleotide sequence but their DNA binding properties are distinct. Finally, I demonstrate that the activators of T3SS gene expression from Photorhabdus luminescens, Aeromonas hydrophila, and Vibrio parahaemolyticus are also sensitive to mutations that disrupt the ExsA-consensus binding site.

ABOUT JESSICA:

Jessica grew up in East Moline, Illinois. Along with an older sister, Jami, Jessica was raised by two wonderful and loving parents, David and Bonnie. She graduated from United Township High School in 2002 and then moved to Bloomington-Normal, Illinois to pursue undergraduate studies at Illinois State University. During her sophomore year at ISU, she studied Metallothionein, a metal sequestering protein, in the laboratory of Dr. David Borst. During her junior and senior years, she worked in the laboratory of Dr. Frank Shaw studying gold arthritic drugs. After graduating with a bachelor’s degree, Jessica stayed at ISU to pursue a master’s degree in the laboratory of Dr. Wade Nichols where she characterized the Cu,Zn- and Mn-cofactored Superoxide Dismutases of Haemophilus parainfluenzae.

In the Fall of 2009 she entered the Microbiology PhD program at the University of Iowa. She joined Tim Yahr’s lab in the Spring of 2010 and begin her research on ExsA, the master regulator of the type III secretion system in Pseudomonas aeruginosa. Jessica’s work has led to two co-first author papers defining ExsA interaction at type III secretion system gene promoters and an additional first author paper showing that ExsA and LcrF, the type III secretion system activator in the yersiniae, recognize a similar binding consensus sequence. In addition, she presented her work at multiple conferences including the Midwest Microbial Pathogenesis Meetings in St. Louis, MO and Milwaukee, WI and the ASM General Meetings in New Orleans, LA and Denver, CO.

Outside of lab, Jessica enjoys spending time with her boyfriend, Chris, baking, swimming, watching movies and going to Iowa Hawkeye football games. Jessica also does an uncanny impression of Walter Mondale and is arguably the best student in her aqua zumba class, mainly because she is the only one under the age of 75.