One goal of the work in the laboratory is a clear understanding of the mechanisms that ensure the proper expression of messenger RNAs in eukaryotes. The research focuses on a nuclear mRNA surveillance pathway in eukaryotes that destroys aberrant RNAs before they exit the nucleus. Central to this pathway is a conserved complex of proteins called the exosome that degrades RNA molecules that fail to undergo post-transcriptional processing reactions such as polyadenylation and splicing. A major unanswered question addressed by the research is what components of the nuclear exosome and the associated TRAMP complex are required for the processing and degradation of RNAs in the nucleus. This RNA surveillance system guards against the formation of defective RNA-protein complexes that have toxic effects on cell growth and proliferation. Previous studies identified Rrp6p, a nuclear exoribonuclease component of the exosome and showed that it plays a critical role in degrading aberrant RNAs in the nucleus. More recent evidence indicates that a second complex called TRAMP plays a key role in activating RNA substrates for degradation by the nuclear exosome. Experiments underway in the lab aim to (i) identify the components of the TRAMP complex required for enhancement of Rrp6p activity, (ii) elucidate the role that TRAMP and Rrp6p play in a general and a specific pathway for mRNA degradation.
A second project focuses the public health challenge caused by the resurgence of tuberculosis and the spread of antibiotic resistant strains of the causative agent, Mycobacterium tuberculosis. Tuberculosis kills nearly 2 million people each year and estimates put the worldwide population of infected individuals at nearly 2 billion. A majority of these people (90%) carries latent, asymptomatic infections that reactivate causing disease and spread of M. tuberculosis to uninfected individuals. The latent phase and the slow growth rate of M. tuberculosis limit the effectiveness of existing antibiotics. One approach to treatment of tuberculosis would be to design drugs that inhibit the establishment of the latent phase or reactivate growth under conditions allowing aggressive treatment of the infection. Uncharacterized toxin-antitoxin systems in M. tuberculosis may play a role in the establishment and maintenance of the latent phase of infection. Work in the laboratory is designed to (i) test the hypothesis that activation of these systems induces a static metabolic state in cells, (ii) identify the molecular targets of the toxins and (iii) determine the impact of the loss of Pin-toxin function on M. tuberculosis survival during hypoxia-induced latency. These studies will lay the groundwork for a thorough analysis of the molecular biology of these toxin-antitoxin systems with the goal of designing therapeutic approaches to the treatment of latent M. tuberculosis infections.