RNA SYNTHESIS IN BACTERIA

RNA synthesis in bacteria

A. Steps of transcription

1. Initiation

(a) RNA polymerase binds to DNA and migrates to the promoter

(i) a promoter is a specific DNA sequence that contains a site for transcriptional

initiation—E. coli promoter contain a -10 region and a -35 region that are

important in binding polymerase

(ii) specific interaction between the promoter and RNA polymerase requires

sigma factor

(iii) initial complex between polymerase and promoter is called the closed

complex

(b) RNA polymerase unwinds ~18 bp forming an open complex

(c) first nucleotide, which is almost always a purine, interacts with the open complex

by binding to polymerase and base pairing with the complementary nucleotide

in the template strand

2. Elongation

(a) the second nucleotide binds to the polymerase-template complex and a

phosphodiester bond is formed

(b) sigma factor is released and polymerase moves down the template, unwinding

the template and catalyzing the addition of each successive nucleotide

(c) approximately 12 nucleotides of the growing RNA chain are base paired with the

DNA template during the elongation phase

3. Termination

(a) Termination requires special termination signals

(i) rho-independent termination

(ii) rho-dependent termination

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