Phenylethanolamine-N-methyltransferase catalyzes the formation of epinephrine from norepinephrine, is found in appreciable quantities only in the brain and the adrenal medulla

#Id: 2438

#Unit 3. Fundamental Processes

Rho needs to translocate along RNA from the rut site to the actual point of termination.

#Id: 2439

#Unit 3. Fundamental Processes

The coupling between transcription and translation has important consequences for rho action. Rho must first have access to RNA upstream of the transcription complex and then moves along the RNA to catch up with RNA polymerase. 

#Id: 2440

#Unit 3. Fundamental Processes

In some cases, a nonsense mutation in one gene of a transcription unit was found to prevent the expression of subsequent genes in the unit even though both genes had their own ribosome binding sites, an effect called polarity.

#Id: 2441

#Unit 3. Fundamental Processes

Rho-dependent termination sites within a transcription unit are usually masked by translating ribosomes, and therefore rho cannot act on downstream RNA polymerases. 

#Id: 2442

#Unit 3. Fundamental Processes

Nonsense mutations release ribosomes within the RNA of a multigene operon, though, enabling rho to terminate transcription prematurely and prevent expression of distal genes in the transcription unit even though their open reading frames contained wild-type sequences

#Id: 2443

#Unit 3. Fundamental Processes

The need for rho factor in vitro is variable. Some (rho-dependent) terminators require relatively high concentrations of rho, whereas others function just as well at lower levels.