ALTERING SPECIFIC TELOMERASE RNA TEMPLATE RESIDUES AFFECTS ACTIVE-SITE FUNCTION

The ribonucleoprotein enzyme telomerase synthesizes telomeric DNA by c opying a template sequence in the telomerase RNA. We studied the funct ional roles of specific residues in the Tetrahymena telomerase RNA tem plate region. Unexpectedly, mutation of certain templating residues ca used dramatic effects on specific aspects of the enzyme reaction, incl uding loss of enzymatic fidelity and premature product dissociation. N one of these fundamental changes in enzymatic action are explainable b y altered base-pairing between the telomerase RNA and DNA substrate. T hese influences of specific template bases of the telomerase RNA on en zymatic properties of telomerase provide evidence for critical roles o f these RNA residues in two active site functions-fidelity and DNA sub strate/enzyme interaction.