Constitutive expression of the brg1 gene requires GC-boxes near to the transcriptional start site.

We previously reported that BRG1, an ATPase subunit of SWI/SNF chromatin remodelling complexes, is constitutively expressed and that the alternative ATPase subunit (BRM) is inducibly expressed through differentiation in mammalian cells. In the present study, the regulatory elements that confer constitutive expression on brg1 were explored. First, we analysed the promoter proximal region surrounding its transcriptional start site. Using computer-aided analysis, a TATA-less, GC-rich promoter containing four putative binding sites for Sp1/3 was predicted. One of the putative Sp1/3-binding sites (from -21 to -15 bp) overlapped with a putative YY1-binding site. A gel-shift assay showed that YY1 but not Sp1/3 bound to this sequence and that Sp3 but not Sp1 bound to the other three predicted binding sites. Furthermore, chromatin immunoprecipitation analysis showed that Sp3 and YY1 bound to the promoter region together with TATA-binding protein in vivo. In vivo and in vitro binding assays showed that Sp3 and YY1 interacted with each other. Together, these results suggest that Sp3 and YY1 recruit general transcription factors and facilitate the assembly of a preinitiation complex.