Date of Award

Spring 2013

Document Type

Restricted Thesis

Terms of Use

© 2013 Emma S. Spady. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

Amy Cheng Vollmer

Abstract

The universal stress protein A (UspA) of Escherichia coli is involved in coordinating the bacterium's responses to numerous stresses. While it has been established that UspA is phosphorylated at serine and/or threonine under stressful conditions, particularly during growth stasis, it is unclear what consequences actual phosphorylation of UspA has for stress response. We have been examining the differences in the E. coli transcriptome during heat shock with respect to UspA's phosphorylation through microarray experiments. Though it is physically unconfirmed, we have data supporting our hypothesis that UspA is phosphorylated at its 117ᵗʰ residue, a serine. A mutant allele of UspA, in which this serine was replaced with an unphosphorylatable alanine, was developed and inserted into an E. coli strain lacking the uspA gene. This S117A mutant was compared to wild-type E. coli in a set of microarray experiments to determine the mutant's responses to heat shock. The microarrays can show which genes the S117A mutant allele is unable to regulate to react to this stress. We observed that the S117A UspA mutant expresses higher levels of genes associated with heat stress, even under non-stressful conditions. However, these same genes were transcribed at comparatively low levels when the mutant was heat shocked. While the SI17A UspA mutant was capable of up-regulating these heat shock-associated genes during heat stress, the magnitude of the regulation was much smaller than in wild-type E. coli. The differentially regulated genes themselves did not show a distinct pattern within a known stress regulon. Notably, several fli genes were unusually up-regulated in the untreated S117A UspA mutant, suggesting that UspA, like its paralogues, may playa role in motility. Both metA and metE were up-regulated during heat stress and in the untreated S117A UspA mutant, implying that the phosphorylation is involved in translational control of growth. Together, these results indicate that UspA's phosphorylation at its 117ᵗʰ serine is involved in an upstream general mediation of heat shock response.

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