Specific binding of single-stranded telomeric DNA by Cdc13p of Saccharomyces cerevisiae

Cdc13p is a single strand telomere-binding protein of Saccharomyces cerevis iae; its telomere-binding region is within amino acids 451-693, Cdc13(451-6 93)p, In this study, we used purified Cdc13p and Cdc13(451-693)p to charact erize their telomere binding activity, We found that the binding specificit y of single-stranded TC,, DNA by these two proteins is similar. However, th e affinity of Cdc13(451-693)p to DNA was slightly lower than that of Cdc13p , The binding of telomeric DNA by these two proteins was disrupted at NaCl concentrations higher than 0.3 M, indicating that electrostatic interaction contributed significantly to the binding process. Because both proteins bo und to strand TG,, DNA positioned at the 3 ' end, the 5 ' end, or in the mi ddle of the oligonucleotide substrates, our results indicated that the loca tion of TG,, in single-stranded DNA does not appear to be important for Cdc 13p binding. Moreover, using DNase I footprint analysis, the structure of t he telomeric DNA complexes of Cdc13p and Cdc13(451693)p was analyzed. The D Nase I footprints of these two proteins to three different telomeric DNA su bstrates were virtually identical, indicating that the telomere contact reg ion of Cdc13p is within Cdc13(451-693)p, Together, the binding properties o f Cdcl3p and its binding domain support the theory that the specific bindin g of Cdcl3p to telomeres is an important feature of telomeres that regulate telomerase access and/or differentiate natural telomeres from broken ends.