Actin-related proteins share significant homology with conventional actins and are classified into subfamilies based on the similarity of their sequences and functions. The Arp4 Subfamily of Arps is localized ill the nucleus, and U mammalian isoform, ArpNbeta (also known as BAF53), is a component of the chromatin remodeling and histone complexes. Another isoform identified in humans, ArpNalpha has scarcely been characterized yet. We identified mouse ArpNalpha and showed that ArpNgamma is more similar between humans and mice than ArpNbeta. No difference was observed between ArpNalpha and beta in subcellular localization and interaction with BRM, which is an ATPase subunit of mammalian SWI/SNF chromatin remodeling complex. However, ArpNalpha was expressed exclusively in the brain and its expression was induced during neural differentiation of P19 Mouse embryonic carcinoma cells. ArpNa is the first brain-specific component of a chromatin remodeling complex to be identified. suggesting that ArpNalpha. has conserved and important roles in the differentiation of neural cells through regulation of chromatin structure. (C) 2002 Elsevier Science (USA). All rights reserved.