What is capping in RNA?
Nuclear RNA capping Capping is the first modification made to RNA polymerase II-transcribed RNA and takes place co-transcriptionally in the nucleus as soon as the first 25–30 nts are incorporated into the nascent transcript (6,7).
How does RNA get capped?
Conventional RNA capping (that is, of mRNAs from the host cell and from DNA viruses) requires hydrolysis of the 5′ γ-phosphate of RNA by an RNA triphosphatase, transfer of a GMP molecule onto the 5′-end of RNA by a guanylyltransferase, and methylation of this guanosine by an (guanine-N7)-methyltransferase.
How is the 5 cap added to mRNA?
The 5′ cap is added to the first nucleotide in the transcript during transcription. The cap is a modified guanine (G) nucleotide, and it protects the transcript from being broken down. It also helps the ribosome attach to the mRNA and start reading it to make a protein.
Why is capping done?
5′ capping is essential for mRNA stability, enhancing mRNA processing, mRNA export and translation. After successful capping, an additional phosphorylation event initiates the recruitment of machinery necessary for RNA splicing, a process by which introns are removed to produce a mature mRNA.
What occurs during RNA splicing?
Splicing occurs during protein synthesis, and involves cutting out and rearranging sections of mRNA. Before mRNA is used as instructions to make a protein, it can be cut into smaller sections and re-arranged in a process called splicing.
What is the function of the cap?
CAP functions by binding, in the presence of the allosteric effector cAMP, to specific DNA sites in or near target promoters and enhancing the ability of RNA polymerase holoenzyme (RNAP) to bind and initiate transcription (reviewed in [1]).
Why is the 5 CAP significant?
The 5′ cap has four main functions: Regulation of nuclear export; Prevention of degradation by exonucleases; Promotion of translation (see ribosome and translation);
How is the 5 cap added to nascent RNAs?
5′ Capping While the pre-mRNA is still being synthesized, a 7-methylguanosine cap is added to the 5′ end of the growing transcript by a 5′-to-5′ phosphate linkage. This moiety protects the nascent mRNA from degradation.
What is capping and tailing?
Adding of an unusual nucleotide methylguanosine triphosphate to the 5-end of heterogenous nucleae RNA hn RNA is called capping. Adding of Adenylate residues to the 3-end in a template independent manner is called tailing.
How does CAP help RNA polymerase?
CAP binds to a specific DNA sequence, which is found next to the genes that are activated. As shown below, when CAP binds to DNA, it coaxes RNA polymerase into place, beginning transcription.
How many reactions are involved in RNA capping?
RNA capping involves three enzymatic reactions at the 5′-end of a transcript. How is the RNA 5′ terminus transferred or repositioned between the three active sites?
What is enzymatic capping of RNA?
Enzymatic production of capped RNA is an easy way to improve the stability and translational competence of RNA used for in vitro translation, transfection and microinjection. Alternatively, use of labeled GTP in a reaction provides a convenient way to label any RNA containing a 5′ terminal triphosphate. Advantages of the Vaccinia Capping System
How does viral RNA capping work?
Since the majority of cellular RNA capping takes place in the nucleus, viruses that replicate in the cytoplasm generate their own RNA caps. It is achieved by encoding their own RNA capping machineries or stealing the cap from host mRNA (cap snatching). Viral RNA capping machineries
How do you make cap RNA with analogs?
RNA Cap Analogs. Cap 0 RNA can also be generated by performing in vitro transcription in the presence of the appropriate cap analogs. The advantage of such co-transcriptional capping is a simple one-step workflow. The downside, however, is the lower yield of transcript and the formation of a small fraction of uncapped RNA as discussed above.