Dr. Johnson received his Ph.D. degree in 1983 from Purdue University under the direction of Dr. Ronald Somerville. After further postdoctoral research at Purdue University and with Dr. John Pringle at the University of Michigan, he joined the faculty in Microbiology and Molecular Genetics in 1988.

Research Interests

Our lab studies the mechanisms by which environmental and cellular signals regulate and integrate cell growth, morphogenesis, and transit through the cell cycle. Specifically, we are interested in the roles of the Cdc42p GTPase, the Cdc24p GEF, and their associated signaling molecules in regulating these basic processes in the budding yeast Saccharomyces cerevisiae, and how these signaling proteins are involved in the virulence of the pathogenic yeast Candida albicans. Experimentally, the approaches that we utilize include classical and molecular genetics, in vivo protein localization using Green Fluorescent Protein (GFP) variants (i.e., CFP, YFP, RFP), biochemical techniques to examine protein-protein interactions, and high-throughput morphology assays to screen small molecule libraries. The types of questions and experiments we will be addressing over the next five years include: (1) What is the role of Cdc42 signaling pathways in the budded-to-hyphal morphological transition that is essential for C. albicans virulence?; (2) What small molecules inhibit the budded-to-hyphal transition and thereby inhibit C. albicans virulence; (3) How does Cdc42p regulate multiple signal-transduction pathways during the S. cerevisiae cell cycle?; and (4) What mechanisms regulate the differential subcellular localization of Cdc42p, Cdc24p, and downstream effectors in budded and hyphal cells?

Selected Publications

Johnson, D.I. Cdc42: An essential Rho-type GTPase controlling eukaryotic cell polarity. Microbiol. Mol. Biol. Rev. 1999 Mar;63(1):54-105.

Toenjes, K.A., Sawyer, M.M., Johnson, D.I. The guanine-nucleotide-exchange factor Cdc24p is targeted to the nucleus and polarized growth sites. Curr. Biol.1999 Oct 21;9(20):1183-1186.

Richman, T.J., Sawyer, M.M., Johnson, D.I. Saccharomyces cerevisiae Cdc42p localizes to cellular membranes and clusters at sites of polarized growth.

Muller, O., Johnson, D.I., Mayer, A. Cdc42p functions at the docking stage of yeast vacuole membrane fusion.

Richman, T.J., Johnson, D.I. Saccharomyces cerevisiae Cdc42p GTPase is involved in preventing the recurrence of bud emergence during the cell cycle. Mol. Cell. Biol. 2000 Nov;20(22):8548-8559.

Toenjes K.A., Simpson D., Johnson D.I. Separate membrane targeting and anchoring domains function in the localization of the S. cerevisiae Cdc24p guanine nucleotide exchange factor Current Genetics 2004 May;45(5):257-64.

vandenBerg A.L., Ibrahim A.S., Edwards J.E. Jr, Toenjes K.A., Johnson D.I. Cdc42p GTPase regulates the budded-to-hyphal-form transition and expression of hypha-specific transcripts in Candida albicans. Eukaryotic Cell. 2004 Jun;3(3):724-734

Richman T.J., Toenjes K.A., Morales S.E., Cole K.C., Wasserman B.T., Taylor C.M., Koster J.A., Whelihan M.F., Johnson D.I. Analysis of cell-cycle specific localization of the Rdi1p RhoGDI and the structural determinants required for Cdc42p membrane localization and clustering at sites of polarized growth Current Genetics 2004 Jun;45(6):339-349

Toenjes, K.A., S. Munsee, A. Ibrahim, R. Jeffrey, J.E. Edwards, Jr., D. I. Johnson. Small molecule inhibitors of the budded-to-hyphal-form transition in the pathogenic yeast Candida albicans. Antimicrob. Agents Chemother. 2005. 49:963-972.