Part:BBa_K2912015

Trp_Lysis gene

This part is the coding sequence (CDS) of a cytoplasmic protein TupA (GenBank: BAB07375.1), which catalyzes the conversion of glucuronic acid and L-glutamic acid to polyglucuronic acid and poly-γ-L-glutamic acid.

Usage and Biology

The lysis gene from colicin-producing strains of bacteria encodes the lysis protein which can cause the host cell to lyse as long as the protein is activated. On the basic of its biological function, we can use lysis gene to break our engineering E.coli and release the interior cell contents when it's time to extract our product-shRNA by adding a Tryptophan attenuator between a RBS and lysis gene.

Before the experiment of Trp_Lysis gene. We have done the T7 promotor_lysis gene characterization experiment with IPTG inducing in LB liquid medium(illustrated with Fig.2).

According to the characterization experiment's result, we can draw a conclusion that once the lysis protein is produced by IPTG inducing, their growth will be significantly inhibited.

In our next step, we transformed the expression vector into HT115 (DE3) E.coli by heat-shock method, culturing in LB liquid medium to exact exponential phase. Afterwards, we started a cell growth curve experiment of our engineering E.coli in different tryptophan concentration gradients and then we calculated their survival rate by use (illustrated with Fig.3).

Besides, we also did a culturing in LB solid medium experiment in different tryptophan concentration gradients.(illustrated with Fig.4)

In contrast with T7 promotor_lysis with IPTG inducing group(illustrated with Fig.5).

Compared to T7 promotor-lysis, the Trp_Lysis gene obviously has the advantage which is able to kill the host cell by breaking their structure in a controlled way. In other words, we can switch off or switch on the killing metabolism by controlling the tryptophan concentration of the culture medium, and the concentration critical valve is around 0.3%(if the concentration is more than 0.3%, the killing metabolism will be closed so that the host cells can grow as usual)