Characterizing constitutive promoters across the Proteobacteria

Although research on promoters has spanned decades, the precise prediction of promoter activity from DNA sequence remains a challenge even in model organisms. Recent literature has identified important differences in the core sequence of sigma70 promoters across classes of Proteobacteria as well as a lack of transferability when promoters are moved from host to host. Currently, there is a need for synthetic constitutive promoters spanning a range of expression levels in species outside of Escherichia coli. Additionally, characterization data defining behavior of the same promoter across multiple species would be extremely valuable to the field. Here, we analyzed promoter activity in three classes of Proteobacteria, which enabled us to better understand the sequence elements correlated with a strong promoter in different hosts. In doing so, we identified and characterized constitutive promoters spanning a range of expression in these species for community use and described the portability of a subset of these promoters as they were moved between hosts. These promoter libraries have broad applications as predictable genetic tools to control gene expression in diverse species. This work adds to the toolkit for gene expression in non-model bacteria and is a step towards the larger goal of accurate promoter prediction in a given host from a de novo sequence. ### Competing Interest Statement The authors have declared no competing interest.