We now provide evidence that this POT1-TPP1 activation requires specific interactions with telomerase, rather than it being a DNA substrate-specific effect.     ///    POT1-TPP1 binding to telomeric DNA activates telomerase repeat addition processivity.     ///    "Second, mutation of a conserved glycine, Gly100 in the TEN (telomerase essential N-terminal) domain of TERT, abolished the enhancement of telomerase processivity by POT1-TPP1, in contrast to other single amino acid mutations. "    ///    "Chimeric human-fish telomerases that contained the human TEN domain were active but not stimulated by POT1-TPP1, showing that additional determinants of processivity lie outside the TEN domain. "