At the beginning of our project, the iGEM part library was checked for parts that could be used for the CARTEL^TM AND gate. Since oxygen concentration plays a key role in the tumor microenvironment, we were especially interested in parts containing HREs (Hypoxia Response Elements). Though, since those BioBricks only covered the needs of our project partially, we decided to improve BBa_K1720002 (iGEM15_SCUT-China) and BBa_K1456004 (iGEM14_ATOMS-Turkiye). So we sent in BBa_K2295003, to fulfill the needs further iGEM teams, dealing with hypoxia dependent gene expression, might have.

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.