Transcription is the process by which the information stored in DNA is converted into messenger RNA (mRNA). This process is performed by an enzyme called RNA polymerase and is the first step in gene expression. Here are the steps involved in the commencement of transcription:
- Promoter recognition: The process begins when transcription factors recognize and bind to a specific sequence of DNA known as the promoter region, which is located upstream of the gene to be transcribed. In eukaryotes, the TATA box is a common component of the promoter region.
- Formation of the transcription complex: After transcription factors bind to the promoter, they facilitate the binding of RNA polymerase to the same region. The complete assembly of transcription factors and RNA polymerase II forms a pre-initiation complex (PIC).
- Unwinding of the DNA: RNA polymerase unwinds the DNA double helix to expose the DNA template strand that will be transcribed into RNA.
- Initiation of RNA synthesis: Using the DNA template strand as a guide, RNA polymerase starts synthesizing an RNA molecule. This is done by matching RNA nucleotides with their complementary DNA bases (adenine with uracil, and cytosine with guanine).
- Elongation: After the first few RNA nucleotides have been linked together, the RNA polymerase moves along the DNA template, continuously adding RNA nucleotides to the growing RNA chain.
- Termination: Transcription ends when RNA polymerase encounters a specific sequence of DNA known as the termination signal.
The commencement of transcription is a highly regulated process, as it determines which genes in a cell are expressed and at what levels. Dysregulation of this process can lead to a wide range of diseases, including cancer.
