Research Goals

For the last several years our studies have focused on the enzymatic mechanisms and biological roles of DNA helicases. The bacterium E. coli and the budding yeast S. cerevisiae provide attractive systems in which to pursue these investigations due to the ease of genetic manipulation and the ability to isolate enzymes for biochemical studies. A large body of literature now exists for the enzymes found in E. coli. Yeast helicases, however, have not been as extensively explored at the biochemical level. We are directing our efforts toward characterizing DNA helicases from both E. coli and yeast. The long-range goal of this aspect of our research program is to understand, in enzymatic and molecular terms, the mechanism of action of several selected helicase enzymes, to define their individual roles in DNA metabolism, and to discover proteins that interact with and modulate the activity of these DNA helicases.

The lab also has an interest in the process of DNA transfer via bacterial conjugation, defined as the unidirectional and horizontal transmission of genetic information between bacterial cells.  Conjugation was discovered more than 50 years ago yet we still have only a rudimentary knowledge of the molecular details surrounding this important mechanism for DNA transfer.  Importantly, this mechanism for DNA transfer is largely responsible for the transfer of antibiotic resistance throughout bacterial populations.  Previous studies have shown that DNA transfer begins at a site- and strand-specific nick in the conjugative plasmid.  The double-stranded DNA molecule is then unwound from this nick, presumably by a DNA helicase, and a single-strand of DNA is transferred into the recipient cell.  This laboratory has demonstrated, using the F plasmid as a model, the participation of two F plasmid-encoded proteins, TraIp and TraYp, and one host-encoded protein, integration host factor (IHF), in the nicking reaction; subsequent unwinding has not yet been reconstituted in any system.  The goal of this aspect of our research program is to arrive at a more detailed understanding of the DNA-based reactions that initiate and contribute to the generation of single-stranded DNA for transfer into the recipient cell.

DNA helicases catalyze a reaction that is essential in all aspects of DNA metabolism.

DNA helicases can generally be grouped into two categories -- those that catalyze a 5' to 3' unwinding reaction and those that catalyze a 3' to 5' unwinding reaction.  This stylized drawing depicts a DNA unwinding reaction catalyzed by a helicase with a 5' to 3' polarity.



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