transcription by RNA polymerase II

Definition

Target type: biologicalprocess

The synthesis of RNA from a DNA template by RNA polymerase II (RNAP II), originating at an RNA polymerase II promoter. Includes transcription of messenger RNA (mRNA) and certain small nuclear RNAs (snRNAs). [GOC:jl, GOC:txnOH, ISBN:0321000382]

Transcription by RNA polymerase II is a complex process that involves the synthesis of messenger RNA (mRNA) from a DNA template. This mRNA molecule then serves as a blueprint for protein synthesis. The process can be broken down into several key steps:

1. **Initiation:**
- The process begins with the assembly of a pre-initiation complex (PIC) at the promoter region of a gene. This complex includes RNA polymerase II, general transcription factors (TFs), and other regulatory proteins.
- The promoter region contains specific DNA sequences recognized by TFs, such as the TATA box and the initiator element.
- TFs bind to the promoter and recruit RNA polymerase II to the transcription start site.
- Once RNA polymerase II is bound, the DNA double helix unwinds to expose the template strand.
2. **Elongation:**
- RNA polymerase II moves along the DNA template strand, using it as a guide to synthesize a complementary mRNA molecule.
- The enzyme adds ribonucleotides to the growing mRNA chain, following the base pairing rules (A with U, T with A, C with G).
- The mRNA molecule grows in the 5' to 3' direction, while the DNA template strand is read in the 3' to 5' direction.
- During elongation, RNA polymerase II encounters a variety of challenges, including DNA secondary structures and nucleosomes.
- To overcome these obstacles, it utilizes a range of mechanisms, including the recruitment of elongation factors and post-translational modifications.
3. **Termination:**
- Transcription terminates when RNA polymerase II reaches a specific DNA sequence known as the polyadenylation signal.
- This signal triggers the recruitment of proteins that cleave the newly synthesized mRNA transcript.
- The cleaved mRNA molecule is then capped at its 5' end with a 7-methylguanosine cap and polyadenylated at its 3' end.
4. **Processing and Export:**
- After termination, the mRNA transcript undergoes further processing steps, including splicing, capping, and polyadenylation.
- Splicing removes non-coding regions called introns from the mRNA, leaving only the protein-coding exons.
- Capping protects the mRNA from degradation and promotes its translation.
- Polyadenylation enhances mRNA stability and facilitates its export from the nucleus to the cytoplasm.
- Once processed, the mature mRNA transcript is transported out of the nucleus through nuclear pores and into the cytoplasm.
5. **Translation:**
- In the cytoplasm, the mRNA transcript is translated into a protein by ribosomes.
- Ribosomes read the mRNA codons (three-nucleotide sequences) and use this information to assemble a chain of amino acids.
- This polypeptide chain then folds into a functional protein.

Transcription by RNA polymerase II is a highly regulated process that is influenced by a multitude of factors, including:

- **Transcription factors:** These proteins bind to specific DNA sequences and regulate the initiation and rate of transcription.
- **Enhancers and silencers:** These DNA elements can increase or decrease the level of transcription.
- **Chromatin structure:** The organization of DNA into chromatin can affect the accessibility of genes to RNA polymerase II.
- **Post-translational modifications:** These modifications to RNA polymerase II and other transcription factors can alter their activity.

Transcription by RNA polymerase II is essential for gene expression and is a fundamental process in all eukaryotic organisms. This complex process ensures that the genetic information encoded in DNA is faithfully transcribed into mRNA, which then serves as the blueprint for protein synthesis.'
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Proteins (42)

Compounds (967)