Transcription (genetics)

Transcription (genetics) is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.

Process

Transcription can be explained in 5 major steps: pre-initiation, initiation, promoter clearance, elongation, and termination.

Pre-Initiation

In the pre-initiation step, the RNA polymerase is attached to the DNA at the promoter region, then it forms a transcription bubble which is the region of DNA that is being transcribed.

Initiation

During initiation, the RNA polymerase starts to synthesize the RNA transcript. This process requires a series of transcription factors.

Promoter Clearance

After the first bond is synthesized, the RNA polymerase must clear the promoter. During this time there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation and is common for both eukaryotes and prokaryotes.

Elongation

Once promoter clearance is complete, the RNA polymerase is released from the promoter. The polymerase then proceeds to the elongation phase, during which the RNA transcript is extended.

Termination

Once a gene is transcribed, the prokaryotic polymerase needs to be instructed to disassociate from the DNA template and liberate the newly made RNA. There are two kinds of termination signal: rho-dependent termination and rho-independent termination.

See also

• Gene expression
• RNA polymerase
• Promoter (genetics)
• Transcription factor

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