Elongation (transcription)
The elongation during transcription handling the process through which the majority of the genetic code containing DNA strand of a mRNA is copied. This is the final phase of transcription after the pre-initiation complex has partially resolved and the mRNA has acquired a 5 'cap structure . At this point in time, the transcript is about 10 to 30 bases long and the cap structure already binds the cap-binding complex .
In the elongation phase, RNA polymerase II is part of the elongation complex that is formed by the addition of several proteins. The energy required for elongation is provided by the cleavage of pyrophosphate from the NTPs. As a result, the elongation complex moves along the DNA double strand until the point of termination is reached. Before this, the splicing of the mRNA still interspersed with introns begins .
The elongation complex is the starting point for the regulation of elongation, and it can be slowed down as well as accelerated. An automatic pause is also inserted each time the complex is again in the vicinity of the promoter (after having run through a histone loop ). These regular breaks seem to be important for the coordination of the elongation.
Initiation of elongation
The beginning of the elongation process is marked by the dissociation of the capping enzymes from the polymerase II. Before the main reaction is under complete control of the elongation complex, it must be assembled. First, the A subunit (RPB1) of the polymerase is dephosphorylated on serines 2 and 5; Through this reaction, catalyzed by CTD phosphatase , the Pol-II is able to bind the protein complexes DSIF and NELF. Together with the kinase complex P-TEFb the early elongation complex is complete, whereby DSIF: NELF can cause a break in elongation and P-TEFb counteracts this by phosphorylation of serine-2.
The complete elongation complex consists of the early elongation complex and the TFIIS protein, the FACT complex , the elongation factor ELL , the elongin complex and the transcription factor IIH .
Main reaction
The central reaction during elongation and also during initiation is the elongation of the mRNA following the example of the bound single strand of DNA, here using the example of a U:
+ 
⇒ 
+ PP i
UTP is esterified with RNA, resulting in an extended RNA.
further reading
- Conaway, J./Conaway, R./reactome: RNA Polymerase II Transcription Elongation
Individual evidence
- ↑ Gopinathrao / reactome: Formation of the Early Elongation Complex ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ Gopinathrao / reactome: Formation of RNA Pol II elongation complex ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ UniProt O00267
- ↑ reactome: Recruitment of elongation factors to form elongation complex ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
