Post-Transcriptional RNA Processing: The 5' Cap and the Poly A Tail | SparkNotes (2024)

FAQs

What does the 5 cap and poly-a tail do? ›

5' cap and poly-A tail

Both the cap and the tail protect the transcript and help it get exported from the nucleus and translated on the ribosomes (protein-making "machines") found in the cytosol ‍ .

The mRNA cap is a highly methylated modification of the 5′ end of RNA pol II-transcribed RNA. It protects RNA from degradation, recruits complexes involved in RNA processing, export and translation initiation, and marks cellular mRNA as “self” to avoid recognition by the innate immune system.

The 5' cap protests the newly-synthesized mRNA from degradation. It also assists in ribosome binding to help initiating translation. 3' poly-A tail protects mRNA from degradation, aids in exporting the mature mRNA to the cytoplasm, and is also involved in binding proteins to initiate translation.

5′-end capping occurs very early during Pol II transcription, typically after the synthesis of ∼20 nucleotides of the pre-mRNA. Capping has been linked to splicing and 3′-end processing of the pre-mRNA, and the export of the mature mRNA.

It is processed - intron removed. What is the advantage of the 5' cap and poly A tail? They promote the export of mRNA and protect it from degradation, also it helps with ribosome attachment. Distinguish between exons and introns.

The cap structure at the 5′ end of mRNA is critical for the efficient translation, stabilization, and transportation of mRNAs in eukaryotes. RNA capping is an essential part of the workflow when mRNA synthesized in vitro (in vitro-transcribed or IVT mRNA) for downstream applications related to translation.

The poly-A tail makes the RNA molecule more stable and prevents its degradation. Additionally, the poly-A tail allows the mature messenger RNA molecule to be exported from the nucleus and translated into a protein by ribosomes in the cytoplasm.

The 5' cap indicates the front end of an mRNA molecule during translation. An intron is any nucleotide sequence within a gene that is removed by RNA splicing while the final mature RNA product of a gene is being generated.

Without a 5' cap on the 5' end of mRNA molecules, translation cannot effectively create a mature mRNA to leave the nucleus and be used during protein synthesis.

The poly(A) tail contributes to both the translational status and stability of mRNAs, and it functions as a master regulator of gene expression in the cytoplasm (Figure 1). Specifically, it can act synergistically with the 7-methylguanosine cap (m7Gppp) on the 5′-end of the mRNA to stimulate translation⁹.

What purposes do capping and poly-A tail addition serve for eukaryotic mRNAs? ›

The polyA tail has an important role in mRNA translation and stability [21]. The interaction of PABP (bound to the polyA tail) with the translation initiation factors (bound to the mRNA 5′ cap) forms a “closed loop” or “circular” mRNA that facilitates translation and protects mRNA from degradation [22].

On mRNAs, the poly(A) tail protects the mRNA molecule from enzymatic degradation in the cytoplasm and aids in transcription termination, export of the mRNA from the nucleus, and translation.

5' End Capping

At the end of transcription, the 5' end of the RNA transcript contains a free triphosphate group since it was the first incorporated nucleotide in the chain. The capping process replaces the triphosphate group with another structure called the "cap". The cap is added by the enzyme guanyl transferase.

The eukaryotic translation initiation factor eIF4E binds directly to the 5′ cap. The heterotrimeric eIF4F complex assembles on the 5′ cap, leading to binding of the 40S ribosomal subunit, assembly of the eukaryotic 80S ribosome and translation initiation.

The interaction of DAN with the 5′ cap is greatly stimulated by the presence of a poly(A) tail on RNA substrates. Cap–deadenylase interactions influence the efficiency of deadenylation in vitro, and can be inhibited by both 5′ stem-loop structures in the RNA substrate as well as the cap binding protein eIF4E.

Then an enzyme called poly-A polymerase adds a chain of adenine nucleotides to the RNA. This process, called polyadenylation, adds a poly-A tail that is between 100 and 250 residues long. The poly-A tail makes the RNA molecule more stable and prevents its degradation.

In eukaryotes, the 5′ cap (cap-0), found on the 5′ end of an mRNA molecule, consists of a guanine nucleotide connected to mRNA via an unusual 5′ to 5′ triphosphate linkage. This guanosine is methylated on the 7 position directly after capping in vivo by a methyltransferase.

The poly(A) tail is necessary for the transport of mRNA molecules from the nucleus to the cytoplasm (f*cke & Ohno, ²⁰⁰⁸) and enhances mRNA stability, as deadenylation is the first step in RNA decay pathways (Wang & Kiledjian, ²⁰⁰¹) and translatability through an interaction between poly(A)‐binding protein 1 (PABPC) to ...