Telomere and telomerase evolution in S. cerevisiae - PROJECT ABSTRACT Telomeres, composed of repetitive DNA sequences at the termini of linear chromosomes, serve as protective caps. However, telomeres cannot be fully copied during replication without the ribonucleoprotein enzyme telomerase. Understanding the delicate balance between telomere length and telomerase activity has important implications for two of the biggest human health concerns: aging and cancer. Telomeres have been shown to shorten with age, acting as a “biological clock” limiting the rounds of division a cell can undergo. To circumvent this proliferative limit, over 85% of cancers aberrantly up-regulate telomerase expression. The long-term goal of this work is to understand the evolution of telomeres and telomerase, and how these cellular components contribute to the health and lifespan of an organism. To begin unraveling these broad fundamental questions, two specific lines of inquiry will be undertaken harnessing the powerful genetic manipulability of Saccharomyces cerevisiae. First, a screen for gain-of- function mutations in telomerase RNA will identify novel alleles that lengthen telomeres by increasing enzyme activity. Such gain-of-function mutants will shed new light on how the essential RNA component of telomerase contributes to the overall action of the enzyme. More active telomerase will also permit exploration of whether longer telomeres alter total fitness of the organism. Second, yeast strains will be genetically engineered to circularize each of their 16 linear chromosomes, allowing novel experimental investigation of the advantages and disadvantages of circular chromosomes in a eukaryotic organism. These novel yeast strains will build a foundation for creating an innovative eukaryotic organism with all linear chromosomes circularized, opening the door to explore big picture questions of telomere and telomerase evolution.
