A) Gel separation of products for WT p48/p58 and p48/p58Y345F reactions on ssDNA. The WT enzyme is significantly more active on ssDNA than either mutant. B) Quantified products for WT p48/p58, p48/p58Y345F, and p48/p58Y345C initiation assays. Mutants synthesize 15–35% of WT products on average. Mutant primase synthesizes shorter products on average. Primer-length products in graph below are defined as products 7–10nt in length. Initiation assays were performed anaerobically, with 250nM ssDNA, 1 µM α-32P ATP, 112 µM CTP, 188 µM UTP, 400 nM enzyme in 50 mM Tris, pH 8.0, 3 mM MgCl2, at 37 °C. Quantifications shown are mean ± SD of n ≥ 3 trials, * = 0.001<p<0.005, ** = 0.001<p<0.0005, *** = p<0.0005, student’s t-test.