Radioactive methylation assay with <i>E.</i><i>coli</i> DNA.

<p>On the X-axis, a dilution factor of 0 is the highest concentration of enzyme and corresponds to the highest H³-methyl incorporation. Each subsequent data point contains a two-fold decrease in enzyme concentration. The asterisk designates the LCF and the double dagger designates the HCN. FI = HCN/LCF. A) M.MspI: At a dilution of 1/2⁸, the substrate is fully methylated and no detectable star activity is observed at the highest enzyme concentration, which is 256-fold over saturation, resulting in an FI of ≥256. B) M.AluI: At a dilution of 1/2⁹, the substrate is completely methylated and no detectable star activity is observed at a dilution of 1/2⁰, which is 500-fold over saturation and results in an FI of ≥500. C) M.HaeIII: Full methylation occurs at a dilution of 1/2³, and after a dilution of 1/2¹, the CPMs start to increase indicating star activity. This results in an FI of 4. D) M.BamHI: At a dilution of 1/2⁴, the substrate is fully methylated and after a dilution of 1/2³, the CPMs start to increase indicating star activity, resulting in an FI of 2. E) M.EcoRI and F) M.HpaII: At a dilution of 1/2⁴, the substrate is fully methylated and no detectable star activity is observed at the highest enzyme concentration used, resulting in an FI of ≥16. The slight decrease in CPMs observed in the assay at high concentrations for some enzymes results from the enzymes precipitating out of solution.