The E. coli trp operon contains the 5 genes Trp-EDCBA for the anabolic enzymes to make the tryptophan.

TLS Online TPP Program

#Id: 2293

#Unit 3. Fundamental Processes

Formation of the closed complex, in contrast, is readily reversible: polymerase can as easily dissociate from the promoter as make the transition to the open complex.

TLS Online TPP Program

#Id: 2294

#Unit 3. Fundamental Processes

During initial transcription, the polymerase remains stationary on the promoter, unwinds downstream DNA, and pulls that DNA into itself

TLS Online TPP Program

#Id: 2295

#Unit 3. Fundamental Processes

scrunching model -proposes that DNA downstream from the stationary, promoter-bound, polymerase is unwound and pulled into the enzyme. The DNA thus accumulated within the enzyme is accommodated as single-stranded bulges.

TLS Online TPP Program

#Id: 2296

#Unit 3. Fundamental Processes

Three general models were proposedfor abortive transcription.

TLS Online TPP Program

#Id: 2297

#Unit 3. Fundamental Processes

Two bases in the non-template strand of the –10 element (A11 and T7) flip out from their base-stacking interactions and instead insert into pockets within the s protein where they make more favorable interactions

TLS Online TPP Program

#Id: 2298

#Unit 3. Fundamental Processes

The transition from the closed to the open complex involves structural changes in the enzyme and the opening of the DNA double helix to reveal the template and nontemplate strands. This “melting” occurs between positions –11 and +2, with respect to the transcription start site.