Telomerase RNA biosynthesis and processing.

Telomerase synthesizes repetitive G-rich sequences (telomeric repeats) at the ends of eukaryotic chromosomes. This mechanism maintains the integrity of the genome, as telomere shortening leads to degradation and fusion of chromosomes. The core components of telomerase are the telomerase catalytic subunit and telomerase RNA, which possesses a small template region serving for the synthesis of a telomeric repeat. Mutations in the telomerase RNA are associated with some cases of aplastic anemia and also cause dyskeratosis congenita, myelodysplasia, and pulmonary fibrosis. Telomerase is active in 85% of cancers, and telomerase activation is one of the first steps in cell transformation. The study of telomerase and pathways where this enzyme is involved will help to understand the mechanism of the mentioned diseases and to develop new approaches for their treatment. In this review we describe the modern conception of telomerase RNA biosynthesis, processing, and functioning in the three most studied systems - yeast, vertebrates, and ciliates.