Fig. S1.

Mechanism for incorporation of sequence heterogeneity into S. pombe telomeres (6–8). (Left) Telomere repeat addition is templated by 3 bp formed between the telomere end and the TER1 template. This alignment leaves the terminal adenine unpaired and contributes to the stuttering reaction that produces variable guanine tracts in S. pombe. (Right) If reverse transcription proceeds into the 5′ TBE, then a cytosine is added to the end of the core 5′-GGTTACA-3′ repeat to generate 5′-GGTTACAC-3′, which causes a nonstuttering register after translocation (underlined C is the rare cytosine incorporated by TBE read-through).