FIG 8 .

CsrA represses translation of ORF27 and iraD via translation coupling. (A) Translational coupling model. CsrA-mediated repression of ORF27 translation leads to repression of iraD translation via translational coupling. Critical GGA motifs of CsrA binding sites BS1 to BS4 (red) and the iraD start codon are also marked. The ORF27 start and stop codons are boxed in yellow. The ORF27 and iraD SD sequences are marked. (B) β-Galactosidase activities ± standard deviations of WT and stop codon mutant ORF27'-'lacZ and iraD'-'lacZ translational fusions determined in vitro with PURExpress. "stop" indicates an ORF27 start-to-stop codon mutation. Experiments were performed at least three times. Values are reported as (1,000)(optical density at 420 nm [OD₄₂₀]) in a 12.5-min reaction. Symbols: solid blue, wild-type (WT) ORF27'-'lacZ fusion; striped blue, stop codon mutant ORF27'-'lacZ fusion; solid black, WT iraD'-'lacZ fusion; striped black, stop codon mutant iraD'-'lacZ fusion. (C) β-Galactosidase activities (Miller units) ± standard deviations of P1-P2-ORF27'-'lacZ and P1-P2-iraD'-'lacZ translational fusions determined in WT (+) and csrA::kan mutant (–) strains during exponential-phase and stationary-phase growth. Experiments were performed at least three times. Symbols: blue, WT ORF27'-'lacZ fusion; black, WT iraD'-'lacZ fusion; red, iraD'-'lacZ fusion with an ORF27 stop codon mutation.