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J. Biol. Chem., Vol. 281, Issue 7, 3773-3784, February 17, 2006
Basic Residues in the Nucleocapsid Domain of Gag Are Required for Interaction of HIV-1 Gag with ABCE1 (HP68), a Cellular Protein Important for HIV-1 Capsid Assembly*From the Department of Pathobiology and the Department of Medicine, University of Washington, Seattle, Washington 98195 During human immunodeficiency virus, type 1 (HIV-1) assembly, Gag polypeptides multimerize into immature HIV-1 capsids. The cellular ATP-binding protein ABCE1 (also called HP68 or RNase L inhibitor) appears to be critical for proper assembly of the HIV-1 capsid. In primate cells, ABCE1 associates with Gag polypeptides present in immature capsid assembly intermediates. Here we demonstrate that the NC domain of Gag is critical for interaction with endogenous primate ABCE1, whereas other domains in Gag can be deleted without eliminating the association of Gag with ABCE1. NC contains two Cys-His boxes that form zinc finger motifs and are responsible for encapsidation of HIV-1 genomic RNA. In addition, NC contains basic residues known to play a critical role in nonspecific RNA binding, Gag-Gag interactions, and particle formation. We demonstrate that basic residues in NC are needed for the Gag-ABCE1 interaction, whereas the cysteine and histidine residues in the zinc fingers are dispensable. Constructs that fail to interact with primate ABCE1 or interact poorly also fail to form capsids and are arrested at an early point in the immature capsid assembly pathway. Whereas others have shown that basic residues in NC bind nonspecifically to RNA, which in turn scaffolds or nucleates assembly, our data demonstrate that the same basic residues in NC act either directly or indirectly to recruit a cellular protein that also promotes capsid formation. Thus, in cells, basic residues in NC appear to act by two mechanisms, recruiting both RNA and a cellular ATPase in order to facilitate efficient assembly of HIV-1 capsids.
Received for publication, July 5, 2005 , and in revised form, October 6, 2005. * This work was supported by National Institutes of Health (NIH) Grant R01 AI048389 (to J. R. L.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 2 Recipient of a Magnuson Fellowship from the University of Washington. 3 Recipient of NIH Grant T32 AI007509-08. 4 Recipient of NIH Grant T32 CA09229. 1 To whom correspondence should be addressed: Dept. of Pathobiology, Box 357238, University of Washington, 1959 NE Pacific St., Seattle, WA 98195. Tel.: 206-616-9305; Fax: 206-543-3873; E-mail: jais{at}u.washington.edu.
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