The binding of the enzyme RNA polymerase to DNA is the prerequisite for the initiation of transcription.
The specific region on the DNA where the RNA polymerase enzyme binds is known as promoter region.
There are two base sequences on the coding DNA strand which the sigma factor of RNA polymerase can recognize for the initiation of transcription.
(a) Pribnow box (TATA box):
It consists of 6 nucleotide bases (5’ TATAAT 3’) located on the left side about 10 base pairs away (upstream) from the starting point of transcription.
(b) The -35’ sequence:
This is the second recognition site in the promoter region of DNA. It contains a base sequence TTGACA, which is located about 35 bases (upstream) away on the left side from the site of transcription start.