Initiation of transcription
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Initiation of transcription is the first step in transcription (genetics). It is an astoundingly complex process that involves numerous multisubunit complexes and large segments of DNA.
In initiation:
- The RNAP recognizes the promoter region of the gene and binds to the DNA at that specific location. At this stage, the DNA is still double-stranded and called closed complex.
- Promoter binding is a two step process. Binding is much tighter above 15°C
- The DNA is unwound and becomes single-stranded at the initiation site (the -10 promoter region). This is called open complex.
- The DNA is melted (the strands are locally separated), the σ-factor leaves the holoenzyme, and elongation begins.
RNAP prefers to start transcripts with ATP, and to a lesser extent GTP (purine nucleotide triphosphates). UTP, and CTP are disfavoured (pyrimidine nucleotide triphosphates).