High-throughput identification of promoters and screening of highly active promoter-5'-UTR DNA region with different characteristics from Bacillus thuringiensis

In bacteria, both promoters and 5'-untranslated regions (5'-UTRs) of mRNAs play vital regulatory roles in gene expression. In this study, we identified 1203 active promoter candidates in Bacillus thuringiensis through analysis of the genome-wide TSSs based on the transcriptome data. There were 11 types of σ-factor and 34 types of transcription factor binding sites found in 723 and 1097 active promoter candidates, respectively. Moreover, within the 1203 transcriptional units (TUs), most (52%) of the 5'-UTRs were 10-50 nucleotides in length, 12.8% of the TUs had a long 5'-UTR greater than 100 nucleotides in length, and 16.3% of the TUs were leaderless. We then selected 20 active promoter candidates combined with the corresponding 5'-UTR DNA regions to screen the highly active promoter-5'-UTR DNA region complexes with different characteristics. Our results demonstrate that among the 20 selected complexes, six were able to exert their functions throughout the life cycle, six were specifically induced during the early-stationary phase, and four were specifically activated during the mid-stationary phase. We found a direct corresponding relationship between σ-factor-recognized consensus sequences and complex activity features: the great majority of complexes acting throughout the life cycle possess σ(A)-like consensus sequences; the maximum activities of the σ(F)-, σ(E)-, σ(G)-, and σ(K)-dependent complexes appeared at 10, 14, 16, and 22 h under our experimental conditions, respectively. In particular, complex Phj3 exhibited the strongest activity. Several lines of evidence showed that complex Phj3 possessed three independent promoter regions located at -251∼-98, -113∼-31, and -54∼+14, and that the 5'-UTR +1∼+118 DNA region might be particularly beneficial to both the stability and translation of its downstream mRNA. Moreover, Phj3 successfully overexpressed the active β-galactosidase and turbo-RFP, indicating that Phj3 could be a proper regulatory element for overexpression of proteins in B. thuringiensis. Therefore, our efforts contribute to molecular biology research and the biotechnological application of B. thuringiensis.