Transcription*RNA polymerase (from E. coli )

2 ’

CoreSigma factor

Holoenzyme

Transcription

Functions of a prokaryotic promoter:

1. ON/OFF Switch

2. Speed Switch

3. Alignment

Transcription Initiation

Transcriptional Elongation:

Termination of TranscriptionInverted Repeats and Hairpins

• The repeat at right is symmetrical around its center shown with a dot

• A transcript of this sequence is self-complementary– Bases can pair up

to form a hairpin as seen in the lower panel

Termination of Transcription

*Rho-independent termination

factor

Termination of Transcription*Rho-dependent termination

RNA Polymerase binding

*Constitutive or basal level transcription

Allosteric activation of RNA polymerase

Inhibition of transcription

DNA-protein interactions

Negative Control of the lac Operon

Proposed CAP-cAMP Activation of lac Transcription