Stopping the Press: Transcription Termination Explained

If the goal of transcription is to create a specific RNA copy of a gene, then the process must have a clear stopping point. If the enzyme reaches this point and falls off the DNA, then the termination phase has occurred.

If a sequence of C and G bases in the RNA bonds with itself, then it creates a heavy physical structure called a hairpin. If this loop puts mechanical stress on the enzyme, then the enzyme loses its grip and falls off the DNA.

If the RNA sequence itself isn't enough to stop the enzyme, then a helper protein must intervene. If the Rho protein "climbs" the RNA and bumps the polymerase off, then it is responsible for termination.

If the cell needs to know where to cut the new RNA strand, then it looks for a specific code. If the sequence AAUAAA appears, then enzymes are recruited to cut the RNA and end the transcription process.

If termination is the end of the "copying" job, then the builder (polymerase) must leave and the copy (RNA) must be handed off. If the DNA is no longer being read, then the strands will naturally zip back together.

If a stop codon is a signal used by the ribosome during translation, then it does not affect RNA polymerase. If transcription stops at a DNA sequence called a terminator, then stop codons and termination signals are different things.

If the RNA has just been finished but hasn't been processed or edited yet, then it is in its original, "nascent" state. If it is the first version, then it is the primary transcript.

If the enzyme stops too early, then the message is incomplete. If it stops too late, then extra, confusing information is added. If termination is precise, then the resulting RNA will be a perfect functional copy of the gene.

If termination happens because of the RNA's own sequence without outside help, then it is intrinsic. If this involves a hairpin and a weak U-A bond region, then those are its defining structural features.

If the RNA is cut at the poly-A signal, then a "tail" of RNA is left sticking out of the polymerase. If an exonuclease enzyme attaches to this tail and digests it until it hits the polymerase, then it "torpedoes" the enzyme off the DNA.

If DNA is kept inside the nuclear envelope and the ribosomes are outside in the cytoplasm, then the finished RNA must move across the membrane to be used.

If the enzyme needs a chemical instruction to stop, then that instruction must be written in the DNA code. If that specific DNA sequence triggers the end of transcription, then it is called the terminator.

If the cell is efficient, then it will not waste its enzymes. If the polymerase is released intact, then it is free to float until it finds another promoter to start a new round of transcription.

If eukaryotes require multiple enzymes to cut the RNA and a "torpedo" enzyme to stop the polymerase, then their system is more complex. If prokaryotes often use a simple hairpin loop, then the prokaryotic system is the simpler of the two.

If the message needs a protective tail to survive the cytoplasm, then it is added after termination. If this process is called polyadenylation, then the signal that starts it shares that name.

If G-C bonds have three hydrogen bonds and U-A have only two, then U-A pairs are easier to pull apart. If the enzyme is already struggling with a hairpin loop, then a weak U-A region allows the RNA to detach effortlessly.

If the enzyme doesn't stop, then it will keep transcribing into the next gene. If this "read-through" occurs, then the cell wastes resources and produces hybrid RNA that could create toxic or useless proteins.

If the bubble is the small area where DNA is kept open for reading, and if the enzyme has reached the end and left, then the bubble is no longer needed. If the enzyme leaves, then the DNA strands will naturally snap back together.

If the primary transcript contains non-coding "junk" called introns, then they must be cut out. If this editing happens after termination, then it is the process of splicing.

If the goal of transcription is to get the information out of the DNA "vault," then the process is successful when that information exists as a free RNA strand. If that strand is ready to be used, then the dogma continues to translation.