Identification of a novel hSnf5 binding protein

The mammalian SWI/SNF chromatin remodeling complex contains either an ATPase subunit of Brg1 (Brahma‐related gene 1) or hBrm (Brahma) that is responsible for its functions in an ATP‐dependent manner. Meanwhile, a Snf5/Ini1/BAF47 component that is shared by both of the SWI/SNF complexes with either Brg1 or hBrm, which may be involved in remodeling the chromatin conformation of the target genes in vivo. Accumulating genetic evidence has defined Snf5 as a potent tumor suppressor in the humans and mice. Accordingly Snf5 is found inactivated or missing in certain lethal childhood cancers. A novel Snf5 binding protein designated as S5BP was originally scanned from a yeast two hybrid library with Snf5 as bait. The mRNA expression of S5BP was successfully identified in most of the human tissues and all of the mammalian cell lines tested., The binding of S5BP and Snf5 was substantial both in vitro and in vivo. We have further found that both of the N‐terminal 1–57 and the C terminal 193–290 amino acid residues of S5BP are critical in its interaction with Snf5. That these proteins co‐localized in the nucleus as proven by the immunofluorescence staining suggests S5BP could be coexisted with Snf5 in a functional complex and participate in the regulation of its target genes, e.g., the promoter activity of p21. The results imply that S5BP could be functional as a component of the SWI/SNF chromatin remodeling complex via direct interaction with Snf5. Detailed mechanisms will be discussed. (This work was supported by the 973 program from the Ministry of Science & Technology, China (#2004CB518605) and the Natural Science Foundation of China (#90408007).