FIGURE 1.

Translation of RF2 expression is autogenously controlled via a negative feedback loop. (A) The nucleotide sequence of the mRNA frameshift site, showing the ORF1 UGA stop codon (bold), with a 3′ C residue, the UAU E-site codon, the internal Shine–Dalgarno (SD) sequence, and its predicted base-pairing to the 16S rRNA. The structure of the RF2 gene shows the second ORF in the +1 frame relative to ORF1. (B) The frameshift mechanism is in part triggered by a leucyl tRNA wobble base paired in the ribosomal P-site. This unstable codon–anticodon interaction is one of the factors stimulating +1 frameshifting, along with a poor context UGA stop codon terminating ORF1, and a SD sequence within ORF1 that stimulates the +1 nucleotide shift.