Telomerase: Structure and properties of the enzyme, and peculiarities of yeast telomerase

Telomerase is a ribonucleoprotein that extends telomeric ends of chromosomes to counterbalance their natural shortening due to incomplete DNA replication in eukaryotic cells. The core enzyme consists of the catalytic reverse transcriptase subunit TERT ( Te lomerase R everse T ranscriptase) and the RNA subunit TER ( Te lomerase R NA), a short specific region of which serves as a template for synthesis of telomeric repeats. Despite the intensive research of telomerase in different organisms, the mechanism of its action remains unclear. This review focuses on telomerase of yeast Saccharomyces cerevisiae . Unlike ciliate and human telomerases, the yeast enzyme adds only one telomeric repeat to the DNA oligonucleotide (primer), imitating the single-stranded telomeric end of a chromosome, and remains stably bound to it after elongation in vitro. This review summarizes the results of numerous studies on the structure and functions of the core enzyme components, their interactions with each other and a primer, and telomerase activity on different substrates in vitro. The peculiarities of telomerase functioning in a cell and accessory proteins of the telomerase complex are also discussed.