Abstract
The telomere is present at the ends of all eukaryotic chromosomes and usually consists of repetitive TG-rich DNA that terminates in a single-stranded 3′ TG extension and a 5′ CA-rich recessed strand. A biochemical assay that allows the in vitro observation of exonuclease-catalyzed degradation (resection) of telomeres has been developed. The approach uses an oligodeoxynucleotide that folds to a stem–loop with a TG-rich double-stranded region and a 3′ single-stranded extension, typical of telomeres. Cdc13, the major component of the telomere-specific CST complex, strongly protects the recessed strand from the 5′→3′ exonuclease activity of the model exonuclease from bacteriophage λ. The isolated DNA binding domain of Cdc13 is less effective at shielding telomeres. Protection is specific, not being observed in control DNA lacking the specific TG-rich telomere sequence. RPA, the eukaryotic single-stranded DNA binding protein, also inhibits telomere resection. However, this protein is non-specific, equally hindering the degradation of non-telomere controls.
Highlights
Tightly bind single-stranded DNA [10,11,20]
The CST complex has similarities to the replication protein RPA, the eukaryotic single-stranded DNA binding protein, and it has been suggested that CST is a telomere-specific RPA-like complex [18]
The overlap in characteristics of RPA and CST makes the presence of RPA at telomeres unsurprising, the interplay between the two proteins remains uncertain, in particular, their individual roles in protecting chromosome ends from resection by exonucleases
Summary
Tightly bind single-stranded DNA [10,11,20]. Structural similarity is apparent between several of the component sub-units of the CST and RPA complexes [21,22], a clear difference is the dimeric nature of Cdc13, a feature absent from RPA1 [23,24,25,26,27]. The CST complex has similarities to the replication protein RPA, the eukaryotic single-stranded DNA binding protein, and it has been suggested that CST is a telomere-specific RPA-like complex [18]. Cdc13 and RPA Protect Telomeric DNA from Resection tightly bind single-stranded DNA [10,11,20].
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