Linear-After-The-Exponential (LATE)-PCR: Primer design criteria for high yields of specific singlestranded DNA and improved real-time detection

Traditional asymmetric PCR uses conventional PCR primers at unequal concentrations to generate single-stranded DNA. This method, however, is difficult to optimize, often inefficient, and tends to promote nonspecific amplification. An alternative approach, Linear-After-The-Exponential (LATE)-PCR, solves these problems by using primer pairs deliberately designed for use at unequal concentrations. The present report systematically examines the primer design parameters that affect the exponential and linear phases of LATE-PCR amplification. In particular, we investigated how altering the concentration-adjusted melting temperature (T-m) of the limiting primer (T-m(L)) relative to that of the excess primer (T-m(X)) affects both amplification efficiency and specificity during the exponential phase of LATE-PCR. The highest reaction efficiency and specificity were observed when T-m(L) - T-m(X) >= 5 degrees C. We also investigated how altering T-m(X) relative to the higher T of the double-stranded amplicon (T-m(A)) affects the rate and extent of linear amplification. Excess primers with T-m(X) closer to T-m(A) yielded higher rates of linear amplification and stronger signals from a hybridization probe. These design criteria maximize the yield of specific single-stranded DNA products and make LATE-PCR more robust and easier to implement. The conclusions were validated by using primer pairs that amplify sequences within the cystic fibrosis transmembrane regulator (CFTR) gene, mutations of which are responsible for cystic fibrosis.