Figure 2. PCR titration of Taq DNA polymerase enzyme. The cleared lysate was diluted 1:10, 1:100, 1:200, 1:400, and 1:800 with 1X PCR reaction buffer (50 mM KCl, 10 mM Tris-HCl, pH 9.0, 0.1% Triton X-100) for the activity assay. One uL of diluted enzyme was added to 20 uL of reaction mix containing 0.2 mM dNTPs, 2 mM MgCl2, 2.5 uM of each URA3 primer, and 40 ng of template DNA in 1X PCR reaction buffer. PCR conditions consisted of 35 cycles: 1 min. at 94 ^oC, 2 min. at 55 ^oC, and 3 min. at 72 ^oC using an MJ Research MiniCycler ( MJ Research, Inc., Watertown, MA , USA). Lane 1 is the PCR product from undiluted cell lysate. Lanes 2 through 6 are PCR products from the dilutions specified above. Lane 7 is a positive control . The 0.6 kb URA3 amplification product is indicated by the arrow.