Small Interfering RNA

The central dogma of molecular biology states that DNA is transcribed to RNA, which in turn is translated to protein. However, only about 2% of RNAs code for proteins. About 98% of the human transcripts are estimated to be non-protein coding, hence referred to as noncoding RNAs. Among the noncoding RNAs are the small noncoding RNAs, known as microRNAs (miRNAs). These RNAs are around 18–25 nucleotides in length and are usually single-stranded. However, they can be double-stranded and have hairpin structures (Zhao et al. 2015). microRNAs are generated from endogenous transcripts (Zhao et al. 2015; Fire et al. 1998). The biogenesis miRNA is shown in Fig. 8.1. miRNAs have the ability to interfere with gene expression at both transcriptional and post-transcriptional (via translation inhibition) levels (Hamilton and Baulcombe 1999; Bernstein et al. 2001) (Fig. 8.1). Thus, they are silencing gene expression via the RNA interference (RNAi) pathway.