Comparison of telomere structure in eukaryotes

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 ۲۰ and ۱۰۰۰ repeat. There is a G-rich strand which is replicated by lagging strand synthesis creating a ۳’ 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, Rap۱ binds the double-stranded telomeric sequences and also binds Rif۱ and Rif۲ which regulate telomere length. Cdc۱۳ and the Cdc۱۳-interacting factors Ten۱ and Stn۱ bind to the single strand overhang. In Saccharomyces Pombe telomeres, Taz۱ binds the dsDNA and also Rap۱ and Rif۱ bind to the ds region via Taz۱. Pot۱ interacts with Tpz۱ and binds to the ۳′ overhang. Poz۱ connects the dsDNA binding complex Taz۱/Rap۱ to the ssDNA binding complex Pot۱/Tpz۱. Ccq۱ also interacts with Tpz۱, recruits telomerase. Stn۱/Ten۱ complex binds to single strand telomere. In mammalian telomeres, the shelterin complex bind double stranded-telomeric DNA consists of six subunits: TRF۱ and TRF۲ which bind directly the double-stranded telomeric DNA. TPP۱ and POT۱ bind single-stranded DNA.TIN۲ connects the dsDNA binding complex TRF۱/TRF۲ to the ssDNA binding complex POT۱/TPP۱. Rap۱ binds the telomere by interacting with TRF۱ and TRF۲. 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.

کلیدواژه ها:

Telomere ، Shelterin ، T-Loop structure