RNA interference, microRNA, and piRNA {small silencing RNA} silence genes.
After viral genes or mobile genetic elements express, double-stranded RNA can catabolize their mRNA {RNA interference} {RNAi}. When extra gene copies insert into organisms, double-stranded RNA suppresses expression.
short interfering RNA
Dicer enzyme hydrolyzes double-stranded RNA to make 22-base-pair double-stranded RNA {short interfering RNA} {small interfering RNA} (siRNA). siRNA has unpaired nucleotides at ends. Proteins {Argonaute protein} can bind to siRNA ends. siRNA unlinks its two strands. One strand binds to proteins {RNA-inducing silencing complex} (RISC). RISC tries to bind to mRNA. If binding is good, Slicer enzyme splits mRNA, which leaves RISC. If binding has short mismatched regions, mRNA stays bound to RISC. Both cases have no translation.
evolution
RNAi began in plant, animal, and fungi common ancestor, one billion years ago, to protect against viruses and mobile genetic elements.
experiments
Using RNAi, researchers can destroy gene mRNA and study results.
RNAi can regulate growth and development using regulatory double-stranded RNA {microRNA} precursors, which Dicer makes into microRNA. MicroRNA has same metabolism as siRNA. Two hundred microRNA genes include JAW, lin-4, and let-7. Small RNA and protein numbers are approximately the same.
RNA {piRNA}, with 25 to 30 nucleotides, binds to Piwi protein in mammal male germ cells, especially at meiosis, making 20000-base to 90000-base clusters {piRNA complex} (piRC). Piwi protein is homologous to Argonaute protein.
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Date Modified: 2022.0225