Total RNA is composed of large amounts of unwanted transcripts, such as ribosomal RNA (rRNA), which accounts for 80-98% of a total RNA sample, and globin mRNA, which accounts for 35-80% of the mRNA in blood samples. Ribosomal RNA is a type of non-coding RNA that is the main component of ribosomes, essential to all cells. Ribosomal RNA is transcribed from ribosomal DNA (rDNA) and then bound to ribosomal proteins to form small and large ribosomal subunits. rRNA is the physical and mechanical component of the ribosome that forces the transfer RNA (tRNA) and messenger RNA (mRNA) to process and translate them into proteins.

Depletion of ribosomal RNA (rRNA) before RNA sequencing (Seq-RNA) is therefore essential and allows us to focus on the analysis of the portions of interest in the transcriptome. The use of oligo dT primer to capture the polyadenylated 3′ tail of transcripts and isolate the mRNA is common in many RNA sequencing preparations; however, this method does not allow processing of degraded samples where most of the RNA is separated from the 3′ tail, nor does it allow isolation of non-polyadenylated transcripts such as ncRNAs. Ribosomal removal methods address these problems by directly depleting rRNA while leaving other transcripts intact.