FIG. 1.

Outline for measuring the size of telomeric 3′ G-rich overhang using the overhang protection assay. Total genomic DNA is incubated with T4 gp32 and GST-UP1, which bind to single-stranded 3′ G-rich overhangs. After the proteins are cross-linked to DNA, unprotected double-stranded DNA is removed by DNase I digestion. After heat inactivation of the DNase I, cross-linking is reversed and proteins are digested to make the protected overhangs available for hybridization to ³²P-labeled C-rich probe. Overhangs are finally size fractionated on a native polyacrylamide gel.