David Friedman

David I. Friedman, M.D.

Emeritus Professor

Areas of Interest

Host-Virus interactions in regulation of gene expression and viral contribution to bacterial pathogenesis

This laboratory uses bacteria to study basic questions relating to gene expression and applies this knowledge to the study of the expression of a bacterial virulence factor. Current interest focuses on two areas: (1) factors influencing modulation of transcription elongation and (2) regulation of expression of Shiga toxin from resident prophages. Phage lambda and other members of the lambdoid family of phages and their Escherichia coli host serve as the model system for these studies.

Transcription elongation: Expression of the early genes of phage l is regulated by the viral encoded N protein. Together with a group of host proteins, called Nus, N modifies RNA polymerase through an RNA signal, NUT, rendering the transcription complex resistant to downstream termination signals. This results in highly processive transcription reading through transcription terminator kilobases from the NUT site. This laboratory studies the role of all three elements of the antitermination complex and their interactions that result in read-through of transcription termination signals.

Shiga-like toxin: One serious public health problem that is of current concern is the infections caused by certain Escherichia coli strains, called Shiga toxin encoding E. coli (STEC). These strains have been implicated in outbreaks of hemorrhagic diarrhea that in some cases lead to serious sequelae such as severe kidney disease and even death. The major contributor to the virulence of these bacteria are the products of genes encoding Shiga toxin (Stx), a glucosidase that destroys ribosomal RNA of eukaryotic cells resulting in a loss of protein synthesis. The genes encoding Stx are carried in the genomes of resident prophages of the lambda family. We are exploiting the extensive knowledge gained over the years on the biology of lambdoid phages to characterize these stx-carrying phages. In particular, we are exploring how phage-encoded functions contribute to toxin expression and release.

Published Articles or Reviews

Waldor, M.K. and Friedman D.I. (2005). Phage regulatory circuits and virulence gene expression.Curr. Opin. Microbiol. 8:459-465.

Tyler, J.S., Mills, M.J., and Friedman, D.I. (2004) The operator and early promoter region of the Shiga toxin type 2-encoding bacteriophage 933W and control of toxin expression. J. Bacteriol.186: 7670-7679.

Tyler, J.S. and Friedman, D.I. (2004). Characterization of a eukaryotic-like tyrosine kinase expressed by the Shiga toxin-encoding bacteriophage 933W. J. Bacteriol. 186: 3472-2479.

Livny, J. and Friedman, D.I. (2004). Characterizing spontaneous induction of  Stx encoding phages using a selectable reporter system. Molec. Microbiol. 51:1691-1704.

Withey, J.H. and Friedman, D.I. (2003). tmRNA and trans-translation: an overview. Ann. Rev. Microbiol. 57: 101-123.

Neely, M.N. and Friedman, D.I. (2003). Analyzing Transcription Antitermination in Lambdoid Phages Encoding Toxin Genes. Methods in Enzymology 371:418-438.

Withey, J,H, and Friedman, D.I.(2002) The biological roles of trans-translation. Curr. Opin. Microbiol. 5:154-159.

Wagner, P.L., Livny,J,,  Neely, M.N., Acheson, D.W.K, Friedman, D.I. and Waldor, M.K., (2002). Bacteriophage Control of Shiga Toxin 1 Production and Release by Escherichia coliMol. Microbiol.44: 957-970.

Zhou, Y. Mah, T.-F., Greenblatt,  J.,  Friedman, D.I. (2002) Evidence that the KH RNA-Binding Domains Influence the Action of the E. coli NusA Protein. J. Mol. Biol. 318: 1175-1188.

Zhou, Y., Filter,  J.J., Court, D.L., Gottesman, M.E., and Friedman, D.I. (2002). A Requirement  for NusG for Transcription Antitermination in vivo by the l N Protein. J. Bact. 184: 3416-3418.