Document Type : Review Article
Authors
1
Biology Department, Islamic Azad University North Tehran Branch
2
Department of Microbiology, Faculty of Biological Sciences, North Tehran Branch, Islamic Azad University, Tehran, Iran
10.22092/ari.2024.365807.3146
Abstract
Telomeres are DNA-protein complexes located at eukaryotic chromosome ends. Broken chromosome ends fuse to each other; therefore, the role of telomeres is to prevent chromosome end fusion. This particular function of telomeres differentiates normal chromosome ends from double stranded breaks in DNA. Telomeres contain tandemly arrayed, short, repeated sequence. Depending on the organism, the repeated sequence is variable between about 20 and 1000 repeat. There is a G-rich strand which is replicated by lagging strand synthesis creating a 3’ overhang, and also a complementary, C-rich strand, which is replicated by leading strand synthesis. In this study, we aim to compare the structure of telomere in Saccharomyces cerevisiae, Saccharomyces pombe and mammals. In Saccharomyces cerevisiae telomeres, Rap1 binds the double-stranded telomeric sequences and also binds Rif1 and Rif2 which regulate telomere length. Cdc13 and the Cdc13-interacting factors Ten1 and Stn1 bind to the single strand overhang. In Saccharomyces Pombe telomeres, Taz1 binds the dsDNA and also Rap1 and Rif1 bind to the ds region via Taz1. Pot1 interacts with Tpz1 and binds to the 3′ overhang. Poz1 connects the dsDNA binding complex Taz1/Rap1 to the ssDNA binding complex Pot1/Tpz1. Ccq1 also interacts with Tpz1, recruits telomerase. Stn1/Ten1 complex binds to single strand telomere. In mammalian telomeres, the shelterin complex bind double stranded-telomeric DNA consists of six subunits: TRF1 and TRF2 which bind directly the double-stranded telomeric DNA. TPP1 and POT1 bind single-stranded DNA.TIN2 connects the dsDNA binding complex TRF1/TRF2 to the ssDNA binding complex POT1/TPP1. Rap1 binds the telomere by interacting with TRF1 and TRF2. Furthermore, in this study the regulation and comparison of Shelterin will be discussed. Also, when double-strand DNA is broken in mammals, DNA damage response pathways has to be activated. Thereby explaining which repair pathways is used. We finally discuss the T-Loop structure as telomeres in several species have been shown to fold back in a structure called t-loop which is believed to mediate telomere protection.
Keywords
Main Subjects
)