Question

5. How is RNA interference (RNAI) used to regulate gene expression in eukaryotes? 5 pts

Answer 1

RNA interference is a method of gene regulation in eukaryotes post-transcriptionally. It involves silencing of a specific mRNA with the help of a complementary dsRNA molecule that binds to and prevents translation of the mRNA. These regulatory RNA molecules are derived from the various sources and have different names depending on their origin. Those made artificially or produced in vivo from dsRNA precursors are typically called small interfering RNAs (siRNAs). Another group of regulatory RNAs is the microRNAs (miRNAs) are of endogenous origin. Regulatory RNAs are generated from longer RNA molecules by the enzyme Dicer into a short double- stranded fragment of about 22 nucleotide pairs. One of the two strands is degraded, while the other strand, which is the miRNA, forms a complex with one or more proteins; the miRNA allows the complex to bind to any mRNA molecule with seven to eight nucleotides of complementary sequence. These small RNAs inhibit expression of complementary target genes in three ways: they trigger destruction of the mRNA encoded by the target gene, they inhibit translation of the mRNA, or they induce chromatin modifications within the target gene and thereby silence its transcription. Silencing machinery includes a complex called the RNA-induced silencing complex (RISC). A RISC contains, in addition to the small RNA, various proteins including a member of the Argonaute family. Argonaute is the catalytic subunit that performs the initial mRNA cleavage and is often called Slicer and mRNA cleavage is called slicing.