Identification of a nuclear protein ArpN as a component of human SWI/SNF complex and its selective association with a subset of active genes

The hSWI/SNF complex remodels the chromatin structure to modulate gene expr ession. The hSWI/SNF complex is a multiprotein complex with at least 10 dif ferent proteins in mammals, Tn this study, we identified the 45 kDa subunit of the hSWI/SNF complex as ArpN, an actin-related protein. ArpN has a 36% identity and 50% similarity with the human beta -actin, but cannot be class ified into any known class of actin-related proteins. ArpN is exclusively l ocalized within the nucleus and appears as the unbound, chromatin-associate d, or nuclear matrix associated forms in the nucleus. In the chromatin immu noprecipitation (ChIP) assay, we found the associations of ArpN with the Et s-2 and c-mycP2 promoter regions in HeLa cells. The promoter regions of the hsp70, cyclophilin, P-globin, TdT, and cd4 genes, however, were not associ ated with ArpN. The Ets-2 and c-mycP2 genes are expressed actively in HeLa cells, but beta -globin, TdT, and cd4 genes are inactive, The hsp70 and cyc lophilin genes have a feature of stress-inducibility. These selective assoc iations of ArpN with a subset of active genes support the proposition that the requirement of hSWI/SNF complex in gene activation is gene specific.