hPOT1_OB1_like: A subfamily of OB folds similar to the first OB fold (OB1) of human protection of telomeres 1 protein (hPOT1), the single OB fold of the N-terminal domain of Schizosaccharomyces pombe POT1 (SpPOT1), and the first OB fold of the N-terminal domain of the alpha subunit (OB1Nalpha) of Oxytricha nova telomere end binding protein (OnTEBP). POT1 proteins recognize single-stranded (ss) 3-prime ends of the telomere. A 3-prime ss overhang is conserved in ciliated protozoa, yeast, and mammals. SpPOT1 is essential for telomere maintenance. It binds specifically to the ss G-rich telomeric sequence (GGTTAC) of S. pombe. hPOT1 binds specifically to ss telomeric DNA repeats ending with the sequence GGTTAG. Deletion of the S. pombe pot1+ gene results in a rapid loss of telomere sequences, chromosome mis-segregation and chromosome circularization. hPOT1 is implicated in telomere length regulation. The hPOT1 monomer consists of two closely connected OB folds (OB1-OB2) which cooperate to bind telomeric ssDNA. OB1 makes more extensive contact with the ssDNA than OB2. OB2 protects the 3' end of the ssDNA. A second OB fold has not been predicted in S. pombe POT1. OnTEBP binds the extreme 3-prime end of telomeric DNA. It is heterodimeric and contains four OB folds - three in the alpha subunit (two in the N-terminal domain and one in the C-terminal domain) and one in the beta subunit. OB1Nalpha, together with the second OB fold of the N-terminal domain of OnTEBP alpha subunit and the beta subunit OB fold, forms a deep cleft that binds ssDNA.
Structure:1OTC_A; Oxytricha nova heterodimeric TEBP binds telomeric ssDNA; defined at 3.5A contacts.
Comment:Oxytricha nova TEBP contains four OB folds - three in the alpha subunit (two in the N-terminal domain and one in the C-terminal domain) and one in the beta subunit. Together with the two OB folds of the alpha subunit N-terminal domain, the beta subunit OB fold forms a deep cleft that binds ssDNA.
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