In vitro cleavage of human telomeric repeats by chimeric endonucleases. (a) Schematic representation of cleavage assay. pTR80, 80 TTAGGG repeats were inserted in the TA cloning site of pGEM-T Easy vector. pNTR, a non-telomeric sequence inserted in the same vector (see Methods). (b) Digestion patterns with various chimeric endonucleases. Plasmids (36 ng) were added with about 0.3 μM purified proteins, except for FN-T (about 0.02 μM), and incubated for 2 h at 25°C and separated by agarose gel electrophoresis. Lanes 1 ~ 15: pTR80/Sca I, lanes 16 ~ 30: pNTR/Sca I.