CST complex subunit STN1, also known as OBFC1, is a 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. Recombinant human OBFC1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.