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TLS Online TPP Program

#Id: 2418

he ability of the enzyme to terminate in vitro, however, is strongly influenced by parameters such as the ionic strength and temperature at which the reaction is performed.

#Unit 3. Fundamental Processes #Transcription elongation and termination #Part B Pointers
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TLS Online TPP Program

#Id: 6796

#Unit 3. Fundamental Processes

The pre-miRNA liberated by Drosha is exported to the cytoplasm, where the second RNA cleavage reaction, performed by Dicer, takes place. As with Drosha, 
Dicer selects its cleavage sites using a measuring, rather than sequence-specific, mechanism.
TLS Online TPP Program

#Id: 6797

#Unit 3. Fundamental Processes

Dicer is constructed of three modules: two RNase III domains and a dsRNA-binding domain called the PAZ domain (named for three proteins that contain this domain: Piwi, Argonaute, and Zwille).
TLS Online TPP Program

#Id: 6798

#Unit 3. Fundamental Processes

Dicer will act on any dsRNA, regardless of sequence, and will cleave this molecule 22 nucleotides from its end.  The PAZ domain anchors the 3’ terminus of the substrate RNA to position the active sites of the enzyme 22 nucleotides away in a ruler-like fashion
TLS Online TPP Program

#Id: 6799

#Unit 3. Fundamental Processes

The action of Dicer generates the short RNA molecule that will determine what target RNA is acted upon. The active form of the regulatory RNA is the single-strand form—at this stage called the guide RNA—incorporated into a RISC protein complex.
TLS Online TPP Program

#Id: 6800

#Unit 3. Fundamental Processes

the RNA guide strand recruits RISC to a target RNA. It has been argued that the length of 22 nucleotides is just long enough to specify a single target sequence uniquely in the large genomes of complex eukaryotes using RNA–RNA base pairing.
TLS Online TPP Program

#Id: 6801

#Unit 3. Fundamental Processes

Binding of RISC complexes causes the bound mRNPs to associate with P bodies. Since P bodies are major sites of mRNA degradation where the decapping complex DPC1/DPC2, t5′→3′ exonuclease XRN1, and cytoplasmic exosomes are concentrated, mRNAs bound by several RISC complexes are degraded.