Fig. 4
The replacement of promoter Ppur to release feedback regulation of key enzymes in purine synthesis. a Different strength of promoters selected to release the transcription initiation repression on the pur operon. The translation initial efficiencies of promoters are predicted by RBS calculator v1.1 [27]. The secondary structures formed between 5’-UTR and purE are predicted by DNAMAN. b The relative mRNA expression level of purE and purF genes under different promoters. The relative transcriptional levels are analyzed by quantitative real-time PCR using Ppur as the control. c The effect of promoter replacement on the accumulation of purine intermediates in the W168 strain. d The effect of the promoter replacement on the accumulation of nucleotides in inosine engineered strains. e The accumulation of inosine in the engineered strains. f The accumulation of hypoxanthine in the engineered strains. The promoter Pveg was used to replace Ppur in the strains W168, PN01, PN03, and PN07, separately producing strains PN09 (W168 Ppur::Pveg), PN12 (W168 ΔpurA Ppur::Pveg), PN13 (W168 ΔpurA ΔpupG Ppur::Pveg), and PN14 (W168 ΔpurA Δdrm Ppur::Pveg). All error bars indicate ± SD, n = 3. A value of P less than 0.05 was regarded to be a significant difference from the original promoter Ppur (*, P < 0.05; **, P < 0.01)