RNA fragmentation and reverse transcription
The RNA fragmentation step using the reverse transcription buffer ensures the generation of RNA libraries with optimal insert sizes. The fragment size can be adapted by shorter or longer incubation times. The protocol also allows the use of input RNA that has already been fragmented, as well as heavily degraded low-quality FFPE RNA. In the reverse transcription step, optimized RT enzyme and buffer formulations ensure strand specificity during cDNA generation. Toxic reagents such as actinomycin D, which negatively affects reverse transcription efficiency, is not required.
Second strand synthesis / end-repair / A-addition
The enzyme mix and buffer formulation are optimized to complete second strand synthesis, end-repair and A-addition in a very short time. First, RNA molecules are degraded. Next, cDNA molecules are used as templates to generate a second cDNA strand. Then, blunt double-stranded DNA is generated. Finally, an A-nucleotide is added to the 5' end of the cDNA. A modification of dexoynucleotides, which is needed with the dUTP method, is not required and ensures optimal efficiency of cDNA generation.
Illumina compatible adapter ligation
Strand-specific ligation of Illumina compatible adapters enables fast and efficient generation of RNA-seq libraries with cDNA prepared from the previous library preparation step. The strand-origin information of the initial RNA can be maintained without additional reagents, modified nucleotides or protocol steps. The included ready-to-use adapter plates allow the sequencing of up to 96 different samples by the combination of a unique 8-nucleotide i5 and i7 index barcode.
CleanStart PCR enrichment
The QIAGEN proprietary CleanStart PCR Mix efficiently and uniformly amplifies the RNA-seq library regardless of the G/C content of the template, while also protecting against PCR contamination. The combination of an optimized buffer formulation and a Hotstart HiFi polymerase enzyme ensures low mutation rates and high processivity for the enrichment of an RNA-seq library. The CleanStart decontamination step allows the removal of contaminating material, such as previously generated NGS libraries, to maximize sample purity.