The Effect of the Copy Number of the Telomerase RNA Gene on the Elongation of Telomeres in Saccharomyces cerevisiae

Abstract

Telomeres are repeated sequences at the ends of chromosomes, which promote chromosome stability by preventing the loss of necessary nucleotides from the DNA with successive rounds of replication. Telomeres are elongated by the enzyme telomerase, which has both a protein component and an RNA component. In the yeast Saccharomyces cerevisiae, the TLC1 gene encodes the RNA component of the enzyme. Telomerase RNA interacts with several proteins to perform its function, including the Ku protein, which binds to the end of the DNA and helps to recruit telomerase to the chromosome thereby facilitating the lengthening of chromosome ends. Ku interacts with telomerase RNA at the site of a 48-nucleotide stem-loop on the RNA's structure. Previous experiments have shown that yeast strains engineered to carry two copies of the TLCI gene exhibit higher levels of telomerase RNA than those that have only one copy of the gene. Also, a yeast strain carrying a copy of the mutant tlc1Δ48 gene, which contains a deletion of the 48-nucleotide stem-loop, contains lower levels of telomerase RNA than a strain with the wild type TLC1 gene. This series of experiments is investigating whether the copy number of the telomerase RNA gene affects the elongation of telomeres in S. cerevisiae. In order to determine this effect, the de novo telomere addition of four strains was examined, as were the native telomere lengths of these strains. The assay indicated that the efficiency of telomere elongation was unchanged by increasing the copy number of the wild type gene but was increased upon increasing the copy number of the mutant gene. Analysis of the native telomere lengths showed that increasing the copy number of either the wild type or the mutant gene allowed the cells to maintain their telomeres at a longer length.