S. pombe telomerase RNA: secondary structure and flexible-scaffold function

Abstract

The telomerase RNA-protein enzyme is critical for most eukaryotes to complete genome copying by extending chromosome ends, thus solving the end-replication problem and postponing senescence. Despite the importance of the fission yeast Schizosaccharomyces pombe to biomedical research, very little is known about the structure of its 1212 nt telomerase RNA. We have determined the secondary structure of this large RNA, TER1, based on phylogenetics and bioinformatic modeling, as well as genetic and biochemical analyses. We find that several conserved regions of the rapidly evolving TER1 RNA are important for the ability of telomerase to maintain telomeres, based on testing truncation mutants in vivo, whereas, overall, many other large regions are dispensable. This is similar to budding yeast telomerase RNA, TLC1, and consistent with functioning as a flexible scaffold for the RNP. We tested if the essential three-way junction works from other locations in TER1, finding that indeed it can, supporting that it is flexibly scaffolded. Furthermore, we find that a half-sized Mini-TER1 allele, built from the catalytic core and the three-way junction, reconstitutes catalytic activity with TERT in vitro. Overall, we provide a secondary structure model for the large fission-yeast telomerase lncRNA based on phylogenetics and molecular-genetic testing in cells and insight into the RNPs physical and functional organization.