An excited fluorescent molecule such as GFP or YFP can dispose of the energy from the absorbed photon in either of two ways: 

by fluorescence, emitting a photon of slightly longer wavelength (lower energy) than the exciting light, or 

by nonradiative fluorescence resonance energy transfer (FRET).

TLS Online TPP Program

#Id: 2339

#Unit 3. Fundamental Processes

Amino acid starvation leads to the binding of uncharged tRNAs to the ribosomal A site; this triggers a sequence of events that begins with the binding of an enzyme called stringent factor (RelA protein) to the ribosome. 

TLS Online TPP Program

#Id: 2340

#Unit 3. Fundamental Processes

When bound to the ribosome, stringent factor catalyzes formation of the unusual nucleotide guanosine tetraphosphate (ppGpp); it adds pyrophosphate to the 3 position of GTP, in the reaction.

TLS Online TPP Program

#Id: 2341

#Unit 3. Fundamental Processes

Bacterial promoters

TLS Online TPP Program

#Id: 2342

#Unit 3. Fundamental Processes

The consensus sequence reflects preferred –10 and –35 regions, separated by the optimum spacing (17 bp).

TLS Online TPP Program

#Id: 2343

#Unit 3. Fundamental Processes

Promoters with sequences closer to the consensus are generally “stronger” than those that match less well

TLS Online TPP Program

#Id: 2344

#Unit 3. Fundamental Processes

consensus sequence of TATAAT in which the leading TA and the final T are highly conserved. Upstream sequences around position –35 also have a region of sequence similarity, TTGACA.