Phone: (804) 828-9093
Dept. Fax: (804) 828-9946
e-mail: christie@vcu.edu

Address:
Department of Microbiology & Immunology
Virginia Commonwealth University
PO Box 980678
1101 E. Marshall St., 6-034 Sanger Hall 
Richmond, VA 23298-0678

Lab Web Page

Professional Experience

• A.B., 1973, University of Chicago
• Ph.D., 1978, Yale University
• Postdoctoral Studies: 1978-1979, Stanford University; 1979-1981, Yale University; 1981-1984, University of California, Berkeley

Research Interests:

1. The role of bacteriophages in microbial evolution and pathogenesis

Current studies are directed towards elucidating the mechanism by which helper phages mobilize a family of enterotoxin-encoding pathogenicity islands, SaPIs, in Staphylococcus aureus. The roles of phage- and SaPI-encoded functions in the excision, replication and specific encapsidation of thsee pathogenicity islands are being investigated. Other recent work has included a study of the role of cryptic prophages as a reservoir of new genes for generation of host range diversity of the Shiga toxin-encoding phage in an E. coli O157:H7 strain. We also have an ongoing interest in the roles of lysogenic conversion genes in the P2-related prophages and cryptic prophages. Some of these, like the sopE gene encoded by a P2-related prophage in Salmonella enterica, have been implicated in bacterial virulence. Others, like the nucC gene encoded by a cryptic prophage in Serratia marcescens, have been adapted for the regulation of genes in the bacterial host. We are characterizing lysogenic conversion genes encoded by a number of P2-related phages in order to elucidate the horizontal transfer of these genes and to understand the contributions of these genes to the physiology of the bacterial host.

2. Determinants for DNA binding by a prokaryotic zinc-finger transcription
factor

Many viruses encode transcription factors that alter the specificity of the host transcriptional machinery to direct the synthesis of viral mRNAs. Late gene expression in the P2- related temperate phages is under the positive control of a family of small, phage-encoded transcriptional activators exemplified by P2 Ogr. These proteins constitute a novel class of zinc-binding proteins which bear little sequence or structural similarity to other known prokaryotic transcription factors. Genetic analysis and in vitro binding studies have identified an unusual activator binding site upstream of late promoters which includes an interrupted element of dyad symmetry and is predicted to span three helical repeats of the DNA major groove. We have investigated the binding of these activators to DNA using NucC, a member of the P2 Ogr family encoded by a cryptic prophage in Serratia marcescens. In recent studies, specific DNA determinants important in binding site recognition by NucC were identified using a variety of chemical protection and interference studies, and binding stochiometry was established. NMR-based structural studies of these unusual transcription factors are being carried out in collaboration with Dr. Dean Pountney at Griffith University, Queensland, Australia.

3. RNA polymerase structure and function

Studies of the interaction of phage-encoded functions with the host RNA polymerase has led to new insights into the roles of RNA polymerase subunits. Site-directed mutagenesis and in vitro transcription studies defined a surface on the alpha subunit of E. coli RNA polymerase that is required for activation of transcription by the P2 Ogr family of transcription factors. Studies of a C-terminal deletion of the beta-prime subunit of RNA polymerase that blocked P2 growth led to the discovery that this mutation affects the action of proteins modulating the timing of lysis during phage infection. The specific gene whose altered expression leads to this altered lysis phenotype remains to be identified. 

Selected Publications:

Wood LF, Tszine NY, Christie GE. Activation of P2 late transcription by P2 Ogr protein requires a discrete contact site on the C terminus of the alpha subunit of Escherichia coli RNA polymerase. J Mol Biol. 1997 Nov 21;274(1):1-7.

Winslow RH, Julien B, Calendar R, Christie GE. An upstream sequence element required for NucC-dependent expression of the Serratia marcescens extracellular nuclease. J Bacteriol. 1998 Nov ;180 (22):6064-7.

Julien, B., Pountney, D., Christie, G.E. and Calendar, R.: Mutational analysis of a satellite phage activator. Gene 223:129-134, 1998.

Christie, GE., Temple, LM., Bartlett, BA., Goodwin, TS. Programmed translational frameshift in the bacteriophage P2 FETUD tail gene operon. J Bacteriol. 2002 184:6522-31.

McAlister, V., Zou, C., Winslow, RH., Christie, GE. Purifcation and In Vitro Characterization of the Serratia marcescens NucC Protein, a Zinc-Binding Transcription Factor Homologous to P2 Ogr. J Bacteriol. 2003 185:1808-16.

Christie, G.E., Anders, D.L., McAlister, V., Goodwin, T.S., Julien, B, Calendar, R. Identification of upstream sequences essential for activation of a bacteriophage P2 late promoter. J. Bacteriol. 2003 185:4609-14.

Markov. D., Christie, G. E. Sauer, B., Calendar, R., Park,T., Young, R. and Severinov, K. P2 growth restriction on an rpoC mutant is suppressed by alleles of the Rz1 homolog lysC . J. Bacteriol.186:4628-37, 2004.

Tallent, S.M., Langston, T.B., Moran, R.G., Christie, G.E. Transducing particles of Staphylococcus aureus pathogenicity island SaPI1 are comprised of helper phage-encoded proteins. J Bacteriol. 189:7520-7524, 2007.

Poliakov, A., Chang, J.R., Spilman, M.S., Damle, P.K., Christie, G.E., Mobley, J.A. and Dokland, T. (2008) Capsid size determination by Staphylococcus aureuspathogenicity island SaPI1 involves specific incorporation of SaPI1 proteins into procapsids. J Mol Biol 380:465-475.

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Date Last Modified: 07/10/2008
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