Where are promoters usually located?

a. upstream of the start site

b. downstream of the start site

c. near nucleotide +25

d. near the hairpin loop

e. downstream of the terminator

A. Upstream of the start site

Explanation:

Promoters are the specific DNA sequences that serve as the binding site for the enzyme RNA polymerase and thereby serve in the initiation of the process of transcription. Promoters are mostly present upstream of the start site (towards the 5' end) of a gene and direct the transcription of adjacent segments of DNA. For example, the promoter region in E. coli extends between positions -70 and + 30 and have consensus sequences as -10 and -35 regions. Promoters have specific sequences that determine the efficiency with which an RNA polymerase binds to them.

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