A Convenient and Sensitive Method for Deoxynucleoside Triphosphate Quantification by the Combination of Rolling Circle Amplification and Quantitative Polymerase Chain Reaction

Measurement of four dNTP pools is important for investigating metabolism, genome stability, and drug action. In this report, we developed a two-step method for quantitating dNTPs by the combination of rolling circle amplification (RCA) and quantitative polymerase chain reaction (qPCR). We used CircLigase to generate a single-strand DNA in circular monomeric configuration, which was then used for the first step of RCA reaction that contained three dNTPs in excess for quantification of one dNTP at limiting levels. The second step is the amplification of RCA products by qPCR, in which one primer was designed to be completely annealed with the polymeric ssDNA product but not the monomeric template DNA. Using 1 amol of the template in the assay, each dNTP from 0.02 to 2.5 pmol gave a linearity with r(2) > 0.99, and the quantification was not affected by the presence of rNTPs. We further found that the preparation of biological samples for the RCA reaction required methanol and chloroform extraction. The method was so sensitive that 1 x 10(4) cells were sufficient for dNTP quantification with the results similar to those determined by a radio-isotope method using 2 x 10(5) cells. Thus, the RCA/qPCR method is convenient, cost-effective, and highly sensitive for dNTP quantification.