Determination of β-actin cDNA copy number by efficiency-independent qPCR. (a) Amplification of 130 nt β-actin amplicon from RNA of Dex-treated CEM-C1-15 cells. The samples were either neet (N
= 0, dashed lines) or had admixed β-actin amplicon (N
= 2 × 105, solid lines). (b) Graph of c
U + N
) representing the optimal estimate U from the same experiment. Solid line: Linear regression solution y = -3.134x + 36.8 (R2 = 0.9963), from the optimal T = 1.34 × 105 (marked threshold in part a) and U = 8.9 × 107 (β-actin template copy number derived from 200 ng poly(A)+ cellular RNA).