Identification of Barx2B, a serum response factor-associated homeodomain protein

CC(A/T)(6)GG or serum response elements represent at common regulatory moti f important for regulating the expression of many smooth muscle-specific ge nes, They are multifunctional elements that bind serum response factor (SRF ) and are important for serum induction of genes, expression of muscle-spec ific genes, and differentiation of vascular smooth muscle cells. In the cur rent study, a yeast two-hybrid screen was used to identify proteins from mo use intestine that interact with SRF, A novel homeodomain-containing transc ription factor, called Barx2b, was identified that specifically interacts w ith SRF and promotes the DNA binding activity of SRF. Northern blotting, RN ase protection analysis, and Western blotting revealed that Barx2b mRNA and protein are expressed in several smooth muscle-containing tissues, as well as in skeletal muscle and brain. In vitro binding studies using bacterial fusion proteins revealed that the DNA-binding domain of SRF interacts with a region of Barx2b located amino-terminal of the homeobox domain. The resul ts of these studies support the hypothesis that interaction of SRF with dif ferent homeodomain-containing proteins may play a critical role in determin ing the cell-specific functions of SRF.