(A) Direct labeling of RNA by chemical methods. Red circles are dye molecules.
(B) Direct labeling of RNA by enzymatic methods. X represents appropriately
modified NTPs that are either directly conjugated to fluorophores or contain
functional groups for subsequent chemical conjugation of dyes. RNA pol, RNA
polymerase; polyA pol, polyA polymerase; Capping Enz, 5‘ end capping
enzyme; Klenow, Klenow fragment of DNA polymerase I from E.
coli; Ligase, typically one of the two T4 RNA ligases.24