Figure 3.

Precise discrimination between GTP and dGTP by DNA. (A) Sequences for the GTP-specific deoxyribozyme NTP-G6 and for the dGTP-specific deoxyribozyme dNTP-G4. (B) Plots of the rate constants for NTP-G6 and dNTP-G4 with various concentrations of GTP (filled symbols) and dGTP (open symbols). Circles and diamonds or squares and triangles represent two replicate experiments conducted with GTP or dGTP, respectively. For selection, the G5 pool from the NTP selection was incubated with a mixture of the four dNTPs (1 mM each) for 50–100 hr, and the DNAs that remained unreacted after ligation were isolated by PAGE. The remaining DNAs were incubated with 100 μM GTP for 2 hr, and the phosphorylated DNAs were recovered and amplified as depicted in Fig. 1A. Likewise, the G5 pool from the dNTP lineage was preselected against function with the NTPs and selected for activity in the presence of 100 μM dGTP. Kinetic parameters are summarized in Table 1.