Telomerase: structure and properties of the enzyme, characteristics of the yeast telomerase

Telomerase is a ribonucleoprotein that extends the telomeric ends of the chromosomes to counterbalance the natural shortening due to incomplete DNA replication in eukaryotic cells. The core enzyme consists of catalytic reverse transcriptase subunit TERT (Telomerase Reverse Transcriptase) and RNA subunit TER (Telomerase RNA), a short specific region of which serves as a template for synthesis of the telomeric repeats. In this review we focus on the telomerase from yeast Saccharomyces cerevisiae. Despite the intensive research of telomerase in different organisms, the enzyme mechanism remains unclear. The observed peculiarities of the yeast telomerase is of great interest too. Unlike ciliate and human telomerases, yeast enzyme can add only one telomeric repeat to a DNA oligonucleotide (primer) imitating the single-stranded telomeric end of the chromosome and remains stably bound to it after elongation. This review is an attempt to summarise results of numerous studies of the structure and functions of the core enzyme components, their interactions between each other and with a primer, telomerase activity on different substrates in vitro. Also the peculiarities of the telomerase functioning in a cell and accessory proteins of the telomerase complex are discussed.