CST Complex Subunit STN1 (OBFC1) is a 368 amino acid protein that contains one OB DNA-binding domain. It is a member of the STN1 family. OBFC1 is component of the CST complex, a complex that binds to single-stranded DNA and is required to protect telomeres from DNA degradation. The CST complex binds single-stranded DNA with high affinity in a sequence-independent manner, while isolated subunits bind DNA with low affinity by themselves. In addition to telomere protection, the CST complex has probably a more general role in DNA metabolism at non-telomeric sites.