Fig. 1

Down-regulation of competitive branch pathways via synthetic sRNA for 5-ALA production in E. coli. A Biosynthetic pathway of 5-ALA and regulation of essential branch pathways via synthetic sRNA. The dotted lines represent the target pathways for synthetic sRNA-mediated repression. The bold blue arrow represents overexpression of ALAS encoding by hemA. B The regulatory mechanism and genetic structure of synthetic sRNA. The synthetic sRNA is composed of two parts: a MicC scaffold and a target-binding sequence. The scaffold structure is responsible for recruiting the RNA chaperone Hfq protein that helps to facilitate the hybridization of sRNA and target mRNA as well as mRNA degradation. The target-binding sequence guides the synthetic sRNA to bind its target mRNA. SD means the Shine–Dalgarno sequence. T1/TE, transcriptional terminator (MITRegistry BBa_B0025). P_tet, aTc-inducible tet promoter. The green mRNA sequence represents the synthetic sRNA binding site. The red sequence means a binding sequence that is complementary to the coding sequence that spans the AUG to nucleotide +21 of the target mRNA. C Titer, yield and cell growth of different engineered E. coli strains with down-regulation of essential branch pathways. (+) represents sRNA-mediated down-regulation. Data are presented as mean values +/− SD (n = 3 independent experiments). ***P < 0.001, *P < 0.05, Student’s two-tailed t-test