Practice question

Affinity purification of mRNA using oligo dT relies on reversible hybridization. Binding of poly-A tail to oligo dT is stabilized by high ionic strength, which shields repulsion between negatively charged phosphates and favors base pairing. Elution requires conditions that destabilize hydrogen bonds between A and T. Low salt concentration reduces shielding, increases phosphate repulsion, and weakens duplex stability, causing mRNA to detach and elute. High salt promotes binding, low pH damages RNA, and high temperature is unnecessary and risky for RNA; low ionic strength is optimal for gentle elution.