Identification of the transactivation domain of the human FHL3

Four and a half LIM domain protein 3 (FHL3) has the transactivation and repressor activity, and plays important roles in regulating the expression levels of various genes. In this study, FHL3 was proved to possess the auto-activation ability when constructed into the pGBKT7 plasmid (a GAL4 DNA-binding domain (BD) cloning vector of the yeast two-hybrid system) and transformed into yeast Y190 cells. To determine the transactivation domain of FHL3, five mutants were constructed by sequentially deleting each LIM domain of FHL3 and then inserting them into the pGBKT7 plasmid. After being transformed into yeast Y190 cells, expression levels of the mutants were identified by Western blot analysis. The β-galactosidase assay showed that the mutant without the fourth LIM domain (LIM4) lost the auto-activation ability. Further investigations on the mutants with deleted first or second zinc finger of LIM4 confirmed that the second zinc finger motif in LIM4 was responsible for the auto-activation of FHL3.