POT-3 preferentially binds the terminal DNA-repeat on the telomeric G-overhang

• Published in: Nucleic acids research Vol. 51; no. 2; pp. 610 - 618
• Main Authors: Yu, Xupeng, Gray, Sean, Ferreira, Helder C
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 25.01.2023
• Subjects: Caenorhabditis elegans Proteins - metabolism; DNA - chemistry; DNA, Single-Stranded - genetics; Gene regulation, Chromatin and Epigenetics; Humans; Shelterin Complex; Telomere - genetics; Telomere - metabolism; Telomere-Binding Proteins - metabolism
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkac1203

Eukaryotic chromosomes typically end in 3' telomeric overhangs. The safeguarding of telomeric single-stranded DNA overhangs is carried out by factors related to the protection of telomeres 1 (POT1) protein in humans. Of the three POT1-like proteins in Caenorhabditis elegans, POT-3 was the only member thought to not play a role at telomeres. Here, we provide evidence that POT-3 is a bona fide telomere-binding protein. Using a new loss-of-function mutant, we show that the absence of POT-3 causes telomere lengthening and increased levels of telomeric C-circles. We find that POT-3 directly binds the telomeric G-strand in vitro and map its minimal DNA binding site to the six-nucleotide motif, GCTTAG. We further show that the closely related POT-2 protein binds the same motif, but that POT-3 shows higher sequence selectivity. Crucially, in contrast to POT-2, POT-3 prefers binding sites immediately adjacent to the 3' end of DNA. These differences are significant as genetic analyses reveal that pot-2 and pot-3 do not function redundantly with each other in vivo. Our work highlights the rapid evolution and specialisation of telomere binding proteins and places POT-3 in a unique position to influence activities that control telomere length.