8. How do the results observed in Figure 3 support the authors' interpretation that primase uses the same set of catalytic residues to carry out the first "initiation" step of primer synthesis and subsequent "elongation" steps of primer synthesis? (1 point) Fig. 3. Functional analysis of active-site Pris residues by structure-based alanine mutagenesis. A and B show the result of the primase initiation and elongation assays, respectively. The initiation assay measures the ability of primase to initiate primer synthesis in the presence of singlestrand poly(dT) DNA and ATP. In the elongation assay, an oligo(A) primer is present in the reaction, in addition to poly (d) DNA and ATP; the assay measures the ability of primase to initiate primer synthesis and/or extend an existing RNA primer. Briefly, reaction products were separated by denaturing electrophoresis on polyacrylamide gels and analyzed by phosphorimaging. For each alanine mutant, two different primase concentrations were tested in the initiation assay. The R306A mutant refers to the residue in the PriL-CTD, See Methods for details