Identification and characterization of a bovine sperm protein that binds specifically to single-stranded telomeric deoxyribonucleic acid

Telomere DNA at the physical termini of chromosomes forms a single;stranded 3' overhang. In lower eukaryotes, e.g., ciliated protozoa, this DNA extens ion is capped by specific proteins that have been structurally and function ally characterized. Much less is known about single-stranded telomere DNA-b inding proteins in vertebrates, Here we describe a new protein from bovine sperm designated bsSSTBP that specifically interacts with single-stranded ( TTAGGG)(N) DNA. The bsSSTBP was extracted from nuclei by 0.6 M KCl. The nat ive size of this protein, estimated by gel filtration, was 20-40 kDa. SOS-P ACE of the UV cross-linked complex between bsSSTBP and telomere DNA indicat ed that several polypeptides are involved in complex formation. Bovine sSST B had high specificity toward nucleotide sequence, since single nucleotide substitutions in the (TTAGGG), substrate suppressed binding. The minimal nu mber of (TTAGGC) repeats required for binding of bsSSTBP was 3, and the pro tein recognized linear but not folded DNA structures. We propose that the b sSSTBP participates in telomere-telomere interactions and the telomere memb rane localization observed in mature sperm. In mammals, somatic telomere-bi nding proteins are apparently substituted by sperm-specific ones that may l ead to a structural reorganization of telomere domains to fulfill functions important during meiosis and fertilization.