Susan M. Egan


Research Interests


My primary research interest is understanding the regulation of gene expression (especially positive regulation) at a molecular level.

I am currently an Associate Professor in the Department of Molecular Biosciences, and have been here at KU since August, 1994. I received a Ph.D. in Microbiology from Cornell University in the laboratory of Valley Stewart. I then worked as a post-doctoral fellow in the laboratory of Robert Schleif at Johns Hopkins University. I learned (nearly) everything I know about bacterial genetics from Valley, and learned lots of molecular biology and biochemistry in the Schleif laboratory. I really love it here in Lawrence, and find this department to be a wonderful place to work.

Current Research

Living organisms must have the ability to alter gene expression in response to developmental or environmental cues. Much regulation of gene expression occurs at the level of transcription, the first step in expression. Transcription regulation can be either negative or positive. While the mechanism of negative regulation is easy to guess at (the negative regulator gets in the way of RNA polymerase), it is more difficult to guess how positive regulation works. The mechanism of positive regulation becomes even more complex when one imagines that two or more positive regulators can influence the expression of the same gene, at the same time. Given this, we are studying the details of regulation of an operon that requires two simultaneous positive regulators for full gene expression, the L-rhamnose catabolic genes in Escherichia coli. We are not interested in metabolism of the sugar L-rhamnose per se, but rather use this easy-to-manipulate system to investigate fundamental questions of gene regulation.

Regulation of the L-rhamnose genes involves two positive regulatory proteins: RhaS responds to L-rhamnose availability; while the other (CRP or CAP) signals whether a preferred carbon source is available. We use a combination of genetic, molecular and biochemical techniques to investigate L-rhamnose regulation. We focus on the interactions among the proteins (RhaS, CRP, and RNA polymerase), and between the proteins and DNA. In systems with a single activator protein, the protein directly contacts RNA polymerase. We hope to determine whether both RhaS and CRP directly contact RNA polymerase, or whether one activator functions through the other. Ultimately, we hope to understand how exactly the interactions lead to an increase in transcription. In addition to the basic questions of positive gene regulation, this system is also important based on the sequence similarity of RhaS to the large AraC family of positive regulators. The AraC family includes the regulators of virulence factors in a number of important pathogens. By comparing the mechanism used by RhaS to activate transcription with that used by AraC, a more general picture of this family of proteins will be gained.


Current Graduate Students:
Jason Wickstrum
Visnja Jevtic
Ana Kolin
Recent Publications
Egan, S. M. 2002. Growing Repertoire of AraC/XylS Activators. J. Bacteriol. 184(20):5529-5532.

Wickstrum, J. R. and S. M. Egan. 2002. Ni+-affinity purification of untagged cyclic AMP receptor protein. BioTechniques 33(4):728-730. (Featured in "BioSpotlight," p. 713)

Ruiz R., J. L. Ramos and S. M. Egan. 2001. Interactions of the XylS regulators with the C-terminal domain of the RNA polymerase alha subunit influence the expression level from the cognate Pm promoter. FEBS Letters 491:207-211.

Egan, S. M., A. J. Pease, J. Lang, X. Li, V. Rao, W. K. Gillette, R. Ruiz, J. L. Ramos, and R. E. Wolf, Jr. Transcription activation by a variety of AraC/XylS family activators does not depend on the class-II-specific activation determinant in the N-terminal domain of the RNA polymerase alpha subunit. J. Bacteriol. 182(24):7075-7077.

Holcroft, C. C., and S. M. Egan. 2000. Interdependence of activation at rhaSR by cyclic AMP receptor protein, the RNA polymerase alpha subunit C-terminal domain and RhaR. J. Bacteriol. 182(23):6774-6782.

Bhende, P. M., and S. M. Egan. 2000. Genetic evidence that transcription activation by RhaS involves specific amino acid contacts with sigma 70. J. Bacteriol 182:4959-4969.

Holcroft, C. C., and S. M. Egan. 2000. Roles of cyclic AMP receptor protein and the carboxyl-terminal domain of the a subunit in transcription activation of the Escherichia coli rhaBAD operon. J. Bacteriol 182:3529-3535.

Bhende, P. M. and S. M. Egan (1999). Amino acid-DNA contacts by RhaS: An AraC family transcription activator. J. Bacteriol. 181:5185-5192.

Egan, S. M. & Schleif, R. F. (1994). DNA-dependent renaturation of an insoluble DNA binding protein: Identification of the RhaS binding site at rhaBAD. J. Mol. Biol. 243: 821-829.

Egan, S. M. & Schleif, R. F. (1993). A regulatory cascade in the induction of rhaBAD. J. Mol. Biol. 234: 87-98.

Send e-mail to Dr. Egan:
EMail Susan

Mailing Address:
Dr. Susan M. Egan
8031 Haworth Hall
Dept. of Molecular Biosciences
University of Kansas
Lawrence, KS 66045

Phone:(785) 864-4294
Fax: (785) 864-5294

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