Nucleic Acids Res. 1999 Nov 1;27(21):e31.

Schmidt WM, Mueller MW.

CapSelect: a highly sensitive method for 5' CAP-dependent enrichment of full-length cDNA in PCR-mediated analysis of mRNAs.

Extra cytosine are more frequently added in presence of the 5′ cap. Increasing Mg2+ to 6 mM increases the frequency of addition of more than 1 C, but only moderately. Instead, when adding BSA in the reaction, supplementing it with 1 or 2 mM Mn2+ after 1h, 3-4 extra dC residues are added to most of the first strand cDNAs. Standard reaction: 0.75 μM oligo dT (or 0.25 μM gene-specific RT primer); 50 mM Tris-HCl (pH 8.3); 75 mM KCl; 3 mM MgCl2; 5 mM DTT; dNTPs 1mM each; 0.1 mg BSA; 20 U RNAse inhibitor (Roche), 200 U SuperScript II; 1h at 42 °C.