Practice question

Mammalian messenger RNAs are modified with a 3' polyadenosine tail of 100 to 250 nucleotides added post-transcriptionally. Exploiting this feature, poly-T selection uses paramagnetic beads conjugated with oligo-dT sequences that base-pair with poly-A tails under high salt conditions. Non-polyadenylated rRNA and tRNA fail to bind and are washed away, enriching mRNA fraction for library preparation. This approach is essentially an affinity chromatography strategy based on A-T hybridization. Hydrolysis degrades RNA randomly, size exclusion separates by length without specificity, whereas poly-T selection provides mRNA specificity.