Muting the Message: RNA Interference Explained

If a specific mRNA molecule is complementary to an introduced small RNA, then it will be targeted for destruction. If the mRNA is destroyed, then the protein it codes for cannot be built, resulting in gene silencing.

If a cell identifies double-stranded RNA, which is usually a sign of a viral infection, then it activates a defense mechanism to chop up that RNA. If this defense mechanism is used to silence genes, then it is the rna interference pathway.

If long dsRNA enters the cytoplasm, then it must be processed into smaller pieces to be useful for silencing. If the enzyme Dicer acts as a molecular cleaver to produce fragments of 21-23 nucleotides, then it is the primary processor.

If long dsRNA is cut into short, functional pieces that "interfere" with gene expression, then these pieces are named according to their function. If they are small and interfere, then they are siRNAs.

If the silencing process requires a machine to scan the cytoplasm for target sequences, then it needs a protein-RNA assembly. If the RNA-Induced Silencing Complex (RISC) performs this scanning and cutting, then it is the central complex of rna interference.

If the RISC complex identifies a target, then a specific protein within that complex must act as the "scissors." If Argonaute has the nuclease activity required to break the mRNA backbone, then it is the catalytic engine of rna interference.

If a double-stranded siRNA is loaded into RISC, then only one strand can serve as the template for base-pairing. If the "guide" strand is selected to stay and the "passenger" strand is discarded, then the complex becomes active.

If a knockout removes the DNA gene entirely, it is permanent. If rna interference only destroys the mRNA messages while the DNA remains intact, then the effect is temporary. If the effect can wear off, then it is a "knockdown," not a "knockout."

If the discovery of gene silencing via dsRNA revolutionized molecular biology in 1998, then the researchers responsible were recognized by the Nobel committee. If Fire and Mello conducted the famous "twitching" experiments in worms, then they are the winners.

If a cell produces its own short hairpins to control its internal protein levels, then these are microRNAs (miRNAs). If they follow the same basic pathway as rna interference, then they are the endogenous version of the system.

If siRNA binds perfectly to mRNA, then it triggers immediate cleavage. If miRNA binds with some "mismatches" or "bulges," then it often blocks translation without immediately destroying the mRNA, which is a key distinction in rna interference.

If transcription happens in the nucleus to create mRNA, and the silencing occurs in the cytoplasm by destroying that mRNA, then the regulation happens after the message is "written." If it happens after transcription, then it is post-transcriptional.

If RNA is a negatively charged, unstable molecule, then the body's natural enzymes will destroy it quickly. If it cannot pass through the oily cell membrane on its own, then rna interference therapy requires specialized delivery "vehicles" like nanoparticles.

If the pathway involves cutting dsRNA, forming a complex, using a guide, and cleaving mRNA, then Dicer, RISC, Argonaute, and small RNAs are essential. DNA Polymerase is used for copying DNA, not for RNA interference.

If a researcher wants to see the effect of a missing protein, then they can use siRNA to deplete the mRNA. If this depletion mimics a loss-of-function mutation without actual genomic editing, then it is a standard application of rna interference.

If the mRNA is cut in the middle, then it no longer has a protective cap and tail on both ends. If the ends are exposed, then standard cellular enzymes (exonucleases) will quickly chew up the remaining fragments, finishing the rna interference process.

If a disease is caused by the "over-expression" of a bad protein or a virus, then destroying the relevant mRNA is a logical cure. While this works for viruses and cancer, it cannot fundamentally change a person's anatomical blood type or speed up complex bone growth.

If the RISC complex remains intact after cutting one mRNA molecule, then it can release the pieces and bind to another matching mRNA. If it repeats this cycle, then rna interference is a highly efficient and catalytic process.

If a plant is infected by an RNA virus, then it uses its internal Dicer-like enzymes to target the invader. If the plant successfully silences the viral genome, then it has used rna interference as an immune system.

If the siRNA triggers rna interference against the p53 mRNA, then those messages will be destroyed. If the messages are destroyed, then the ribosomes have nothing to translate into protein. If translation stops, then the protein levels must drop.