We would like to submit BBa_K2561001 for the Best Basic Part award. The BioBrick encodes a sigma factor native to Bacillus subtilis, σF.
Sigma factors are critical transcription factors in bacteria. They are involved in everything from heat shock response to flagellation to general cellular housekeeping [1]. Sigma factors recruit RNA polymerases to bind to specific promoter sequences; sigma factors bind the RNA polymerase and the resulting holoenzyme has the ability to recognize specific sequences. While RNA polymerases tend to be relatively well conserved between species, sigma factors have great diversity. They have an important role in synthetic biology for their ability to have a wide dynamic output, ranging from very low when OFF to very high when ON, making them potent activators of gene expression [2].
σF is a sigma factor from B. subtilis involved in early forespore gene expression in its native host [3]. Bervoets et. al. showed that alternative sigma factors used recombinantly in E. coli, such as σF, are orthogonal and can be powerful tools in synthetic biology as transcriptional activators without being subject to leakiness and noise from native sigma factors. σF does not significantly recognize and bind endogenous E. coli σ70-dependent promoters. In addition, we’ve also submitted a BioBrick to the registry, BBa_K2561002, encoding PF2, a strong promoter recognized by σF. This promoter was developed (synthetically) and characterized by Bervoets et. al. who showed that it is robustly recognized and bound by σF and weakly recognized and bound by E. coli endogenous σ70. Together, our two parts are a new tool for synthetic biologists, providing a robust activator for use in E. coli gene networks that is not subject to leakiness or variations in native sigma factor expression. We hope iGEM teams in the future will be able to use this part to continue to build more complex systems and biocircuits.