Figure 1.

The principle of PhaR regulation and its application in two-hybrid system. (A) PhaR can specifically bind to the phaP promoter to repress its expression, however, when PHB granules are produced, PhaR will prefer to bind PHB and release from the phaP promoter, liberating PhaP expression. (B) PhaR has two separate domains, a DNA binding domain (DBD) and a PHB granules binding domain (GBD), each domain fuses with a protein (X and Y), if × and Y have an interaction, this power will direct to a complex DBD-X:Y-GBD, just like a reconstituted "PhaR", so when PHB granules exist, this reconstituted "PhaR" will drop from DBD binding site and release the expression of LacZ reporter. (C) GBD and its fusions expressed in vivo were insoluble, so PhaP also with a strong PHB binding ability was employed to replace GBD in this study.