SEQUENCE-SPECIFIC DNA PRIMER EFFECTS ON TELOMERASE POLYMERIZATION ACTIVITY

The ribonucleoprotein enzyme telomerase synthesizes one strand of telo meric DNA by copying a template sequence within the RNA moiety of the enzyme. Kinetic studies of this polymerization reaction were used to a nalyze the mechanism and properties of the telomerase from Tetrahymena thermophila. This enzyme synthesizes TTGGGG repeats, the telomeric DN A sequence of this species, by elongating a DNA primer whose 3' end ba se pairs with the template-forming domain of the RNA. The enzyme was f ound to act nonprocessively with short (10- to 12-nucleotide) primers but to become processive as TTGGGG repeats were added. Variation of th e 5' sequences of short primers with a common 3' end identified sequen ce-specific effects which are distinct from those involving base pairi ng of the 3' end of the primer with the RNA template and which can mar kedly induce enzyme activity by increasing the catalytic rate of the t elomerase polymerization reaction. These results identify an additiona l mechanistic basis for telomere and DNA end recognition by telomerase in vivo.