Telomerase is a specialized ribonucleoprotein that maintains genome integrity by adding telomeric DNA to the ends of eukaryotic chromosomes. For many years now, it has been established that the telomerase complex is minimally composed of an RNA molecule, Tlc1, and a reverse transcriptase called Est2p. In the cell, Tlc1 serves as a scaffold for many other proteins (Est1p, Est3p, yKu, Sm7) and add telomeric repeats at shortened chromosome ends by reverse transcribing an essential template within the RNA molecule.
Using mass spectrometry analysis and a native system to purify Tlc1-bound proteins, we have been able to identify new partners for Saccharomyces cerevisiae telomerase. These proteins are components of the RNase P/ RNase MRP complexes; two related, highly conserved and essential RNPs that are involved in the processing of tRNA, rRNA and certain mRNAs. These ribonucleoproteins both contain a catalytic RNA subunit (Rpr1 for RNase P and Nme1 for RNase MRP) that is bound by a group of proteins.
We report that the Pop1, Pop6 and Pop7 proteins of the RNase P/MRP complexes bind to yeast telomerase RNA and are essential constituents of the telomerase holoenzyme. The trio binds to a specific and highly conserved RNA domain present in Tlc1. This domain, called P3 domain, is also shared by the RNAs of RNase P/MRP. The results also show that Pop1/Pop6/Pop7 function is to maintain the essential components Est1 and Est2 on the RNA in vivo. Consistently, addition of Pop1 allows for telomerase activity reconstitution with wild type telomerase RNA in vitro. Thus, the same chaperoning module has allowed the evolution of functionally and, remarkably, structurally distinct RNPs, telomerase and RNases P/MRP, from unrelated progenitor RNAs.
Note: N. Laterreur & B. Lemieux contributed equally to the work..