The physical and functional interplay between telomere and repair proteins: mechanistic and evolutionary insights from an unconventional model

Joan And Sanford I. Weill Medical College Of Cornell University, New York NY

Investigators

Abstract

The physical and functional interplay between telomere and repair proteins: mechanistic and evolutionary insights from an unconventional model The genetic information that the cell uses to encode normal functions resides on thread-like molecules called chromosomes. The tips of these chromosomes, named telomeres, play especially important roles in protecting the integrity of the genetic information. Telomeres can be likened to aglets, the metal or plastic caps at the tips of shoelaces; when the aglets are missing, the shoelaces (chromosomes) become frayed and fall apart. Paradoxically, the DNA at telomeres is difficult to maintain during the process of chromosome duplication, which occurs each time a cell divides. Many protein molecules, working together are required to ensure the proper maintenance of telomere DNA. This research will utilize a variety of techniques to investigate how these protein molecules work together, how they interact with one another, and how these interactions are regulated to promote telomere integrity. The study will be carried out using a fungus called Ustilago maydis, which is easy to manipulate and has telomere features that are shared by many animals. This research will also train many undergraduate students and a postdoctoral student, allowing them to acquire the technical and critical thinking skills necessary for future careers in science. The undergraduates will be recruited from Hostos Community College, an institution that serves primarily under-represented minority students. Training these students will benefit society by promoting a more diverse scientific workforce. Telomeres are specialized nucleoprotein structures that protect and stabilize the ends of chromosomes. Telomere DNA is maintained through periodic addition of a repetitive sequence by a special reverse transcriptase named telomerase. A key function of the telomere nucleoprotein complex is to allow the cells to distinguish normal chromosome ends from double strand breaks by suppressing inappropriate DNA repair. However, repair proteins paradoxically help to promote telomere maintenance in two circumstances. First, telomerase-negative cells can utilize an aberrant recombination/repair mechanism (called ALT) to add telomere repeat tracts onto chromosome ends. Second, in telomerase-positive cells, multiple recombination repair factors promote the maintenance of telomere tracts by enhancing telomere replication (e.g., by stabilizing stalled forks or surmounting replication barriers). We showed recently that both of these functions of repair proteins at telomeres can be faithfully reproduced in Ustilago maydis, a model fungal system for studying fundamental cellular processes. Moreover, we discovered in U. maydis several conserved and functionally significant interactions between telomere proteins and repair factors. Consequently, we are poised to address how the direct physical interactions between telomere and repair proteins channel the enzymatic activity of repair factors to promote telomere maintenance while suppressing aberrant repair. This is a level of regulation that has not received detailed examinations. We have also uncovered in U. maydis two duplex telomere binding proteins with distinct functions and interactions with repair proteins. We will therefore examine how the telomere and repair proteins co-evolve through comparative analysis of these factors in different fungi. Objectives and Methods: 1) Use binding and activity assays to define the molecular basis of telomere-repair protein interactions and examine how the interactions affect the repair activities of these proteins in vitro. 2) Use genetic and cell-based assays to determine the mechanisms and function of the telomere-repair protein interactions in promoting telomere replication and ALT in vivo. 3) Characterize the properties of duplex telomere-binding protein homologs in budding yeast and Ustilago to determine the evolutionary path of duplex telomere-binding proteins and their interaction with repair factors in fungi. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.