As an improved BioBrick we sent in HRE-pTal. Currently there is no BioBrick containing a minimal promoter in addition to the HRE, but only HRE itself (BBa_K1456004) as well as a combination of CMV-HRE-TATAbox (BBa_K1720002).

Since BBa_K1456002 contains a CMV promoter, sensitive oxygen dependent gene expression is not possible. Having a high basal expression downstream of the CMV promoter, BBa_K1720002 is not feasible for many projects. This problem is fixed in BBa_K2295003 by introducing the minimal promoter pTal downstream of the HRE, instead of a CMV promoter upstream of the HRE. However, to remove an EcoRI restriction side, the pTal promoter was slightly modified by changing one base pair.

BBa_K1456004 doesn’t contain a promoter at all. Hence it is not ready to use and a lot of further cloning is involved, before oxygen dependent gene expression can be achieved.
As already mentioned in the “BioBrick Basic Part” section, the introduction of multiple enhancer elements allows highly specific oxygen dependent expression in different cell types. Tuning the amount of enhancer elements, downstream transcription can be regulated.
By having a BglII restriction site in between the HRE and the pTal promoter, we offer an easy cloning strategy to change the amount of multiple enhancer elements. Using compatible end cloning, future iGEM teams will profit a lot from the improvement of BBa_K1720002 and BBa_K1456004.