7

A. ATTENUATION MECI1ANISM

B. TRANSI ATIONAI. INHIBITION

Si gnał metabolitc In n <i*

mRNA

Translaiion

proceeds

Uoditig $equcnce —

” K

Shine Start codon Dalgamo sequencc

.Signal mctabolitc binds

Signal

metabolit?

uuuu

Terminator

PREMATure

1KK\1\AII0X

FIGURĘ 11.18 Riboswitch Mechanisms

Riboswitches alternate between two altema»ive stem and loop structures depending on the presence or absence of the signal metabolite. (A) In the atlenoation mechanism, the presence of the signal metabolite results in formałion of tbe terminator structure and transcripłion is aborted (B) In tbe translational inbibition mechanism, tbe presence of tbe metabolite results in sequestration of tbe Shine-Dalgarno sequence, which prevents translation of the mRNA.