FIG 4.

Operon position can influence gene expression under translation limitation; however, it is independent of transcription-translation coupling. (A) Sketch for GFP and RFP fused in an operon with an intergenic terminator of efficiency y (see the details of the construction in reference 39) and the formula of the expression ratio of GFP to RFP. When the efficiency y is zero, it corresponds to the case without intergenic terminator (see “no ter” in panel B). (B) The expression ratio between downstream GFP and upstream RFP [in the units of RFU(GFP)/RFU(RFP)], as a function of growth rate decreases with increasing Cm concentration. The experimental ratios (symbols) are fit with the same model (lines) on ribosome stalling-induced mRNA degradation used to describe the difference between β-gal and GFP expression in Fig. 3 (see supplemental material). “no ter” and “ter 1 to 4” correspond to terminator sequences of increasing efficiency that can be used to estimate the contribution of transcription-translation coupling (“I21” [no terminator], “R9,” “R17,” “W13,” and “R32,” respectively, in reference 39). The cells were grown in M9 minimal medium containing glucose. Cm was added to a final concentration of 0, 2, or 4 μM.