ACTIVATION AND REPRESSION OF ESCHERICHIA-COLI PROMOTERS

There is no organism in which transcription initiation is better under stood than Escherichia coli. Recent studies using genetics, biochemist ry and structure analysis have revealed how RNA polymerase interaction s at promoters are regulated. Prominent examples include the recruitme nt of polymerase by activators touching its alpha and sigma subunits; which subunit is touched depends on which activator is used and where it binds the DNA. The less-common cases centering on enhancer-dependen t transcription use an entirely different mechanism, involving either DNA looping or tracking.