FIG. 7.

Effects of 3′ dideoxynucleotide substitutions in the DNA primer on cleavage and extension by yeast telomerase. (A) Polymerization reactions were carried out using 160 ng (lanes 1 to 4) or 400 ng (lanes 5 to 8) of the DNA primers (as indicated at the top of the panels) and 5 μg of the DEAE fractions. The primers bear either a deoxy- or a dideoxynucleotide at their 3′ termini. The sequences of the oligonucleotides used are shown at the top, and the GT-rich (yeast telomere-like) parts of the oligonucleotides are underlined. (B) Polymerization reactions were carried out using 0.5 μg of the DNA primers (as indicated at the top of the panel) and 5 μg of the DEAE fractions. The primers used in lane 3, 4, 7, and 8 bear dideoxynucleotides at their 3′ ends. RNase A was added to the reactions in lanes 2, 4, 6, and 8. Products derived from direct extension or cleavage followed by extension (cleavage derived) are indicated by vertical bars to the left of the panels. Bands unaffected or abolished by the dideoxynucleotide substitution are indicated by closed or open circles, respectively.