Regulatory subunit of the ATP-dependent RSF-1 and RSF-5 ISWI chromatin-remodeling complexes, which form ordered nucleosome arrays on chromatin and facilitate access to DNA during DNA-templated processes such as DNA replication, transcription, and repair (PubMed:12972596, PubMed:28801535). Binds to core histones together with SMARCA5, and is required for the assembly of regular nucleosome arrays by the RSF-5 ISWI chromatin-remodeling complex (PubMed:12972596). Directly stimulates the ATPase activity of SMARCA1 and SMARCA5 in the RSF-1 and RSF-5 ISWI chromatin-remodeling complexes, respectively (PubMed:28801535). The RSF-1 ISWI chromatin remodeling complex has a lower ATP hydrolysis rate than the RSF-5 ISWI chromatin-remodeling complex (PubMed:28801535). The complexes do not have the ability to slide mononucleosomes to the center of a DNA template (PubMed:28801535). Facilitates transcription of hepatitis B virus (HBV) genes by the pX transcription activator. In case of infection by HBV, together with pX, it represses TNF-alpha induced NF-kappa-B transcription activation. Represses transcription when artificially recruited to chromatin by fusion to a heterogeneous DNA binding domain (PubMed:11944984, PubMed:11788598). Component of the RSF-1 ISWI chromatin-remodeling complex at least composed of SMARCA1 and RSF1 (PubMed:28801535). Within the RSF-1 ISWI chromatin-remodeling complex interacts with SMARCA1 (PubMed:28801535). Component of the RSF-5 ISWI chromatin-remodeling complex (also called the RSF complex) at least composed of SMARCA5/SNF2H and RSF1 (PubMed:12972596, PubMed:28801535). Within the RSF-5 ISWI chromatin-remodeling complex interacts with SMARCA5/SNF2H; the interaction is direct (PubMed:12972596, PubMed:28801535). Identified in a centromere complex containing histones H2A, H2B and H4, and at least CENPA, CENPB, CENPC, CENPT, CENPN, HJURP, SUPT16H, SSRP1 and RSF1 (PubMed:27499292). Also binds the HBV pX/HBx protein, which is required to activate transcription of the viral genome (PubMed:11944984, PubMed:11788598). Localization is diffuse during mitosis (PubMed:12972596). Co-localizes with SMARCA5 in the nucleus (PubMed:12972596). Experimental confirmation may be lacking for some isoforms. Ubiquitously expressed. Highly expressed in the heart, skeletal muscle, kidney and placenta (PubMed:12972596). Expressed at low levels in the brain and colon (PubMed:12972596). Phosphorylated. Contaminating sequence. Potential poly-A sequence.