FIG. 4.

Some point mutations in TR1-5 and TR26-30 lead to minor shifts in alignment with telomerase. (A) The telomerase allele ter1-3C causes the synthesis of a 26-bp repeat. The presence of the mutation at position 3 of the template causes telomerase alignment to shift by 1 nt, such that alignment begins at a nucleotide 3′ of the normal start site. (B) A 24-bp repeat is synthesized in the strain containing ter1-28G. When a G is copied from position 28, the alignment shifts by 1 nt toward the 5′ end of the template. Base pairing then occurs with positions 2 to 4 of the template. (C) ter1-2G can cause a 27-bp repeat to be synthesized. When a C is present at position 2 of the template, telomerase alignment is sometimes shifted by 2 nt. In this case, only 2 nt of base pairing is apparent between the tip of the telomere and the template.