Figure 8.
Model of metA regulation at the transcriptional and post-transcriptional level. On the left: Under low SAM conditions, transcription from PmetA is increased, the riboswitch is in the SAM-free state, the SD controlled by the riboswitch is accessible and activates translation in the read-through mRNA from the starting codon AUG2. Under these conditions, metA mRNA is destabilized, probably due to RNase access to specific cleavage site(s) in the mRNA. On the right: Under high SAM conditions, transcription from PmetA is decreased, the riboswitch is in the SAM-bound state, the SD controlled by the riboswitch is not accessible and metA translation is repressed. Under these conditions, metA mRNA is stabilized, probably because the riboswitch pseudoknot structure blocks the RNase access [16].