RNA Library Preparation for NGS is an essential process that converts RNA molecules into sequencing-compatible DNA libraries, enabling comprehensive transcriptome profiling. This workflow includes RNA isolation, fragmentation, cDNA synthesis, adapter ligation, and amplification, with protocol choices influenced by RNA characteristics and experimental objectives.
RNA Isolation and Initial Processing
The workflow begins with extracting high-quality RNA from biological samples. Since ribosomal RNA (rRNA) represents up to 90% of total RNA, selective enrichment is required. PolyA selection is used to focus on messenger RNA (mRNA), while rRNA depletion is preferred for studying non-coding RNAs or partially degraded samples.
RNA Fragmentation and Reverse Transcription
Fragmentation is performed to generate appropriately sized RNA pieces for sequencing. This can occur before or after reverse transcription into complementary DNA (cDNA). Common fragmentation techniques include chemical or metal-ion treatment, and enzymatic digestion.
Fragmentation prior to reverse transcription helps ensure more uniform coverage across transcripts, whereas fragmentation after cDNA synthesis may bias sequencing reads toward the 3′ end.
cDNA Synthesis and Adapter Ligation
After fragmentation, RNA fragments are reverse-transcribed into cDNA. Sequencing adapters are then ligated to fragment ends to enable amplification and sequencing. Small RNA-seq workflows often use specific 3′ and 5′ adapter ligation strategies, while standard RNA-seq libraries typically require end repair and phosphorylation before ligation.
Library Amplification and Size Selection
PCR amplification increases library yield, but cycles must be minimized to reduce bias. Size selection using gel electrophoresis or bead-based methods enriches fragments typically between 150–300 bp and removes unwanted adapter dimers.
This workflow produces a high-quality RNA library enabling powerful transcriptomic analyses covering both coding and non-coding RNA species.
