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J. Biol. Chem., Vol. 283, Issue 20, 13780-13791, May 16, 2008

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A Model for Oligomeric Regulation of APOBEC3G Cytosine Deaminase-dependent Restriction of HIV^*

Linda Chelico, Elizabeth J. Sacho, Dorothy A. Erie^¶, and Myron F. Goodman¹

From the Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, California 90089-2910, the Department of Chemistry and ^¶Applied and Materials Sciences Curriculum, University of North Carolina, Chapel Hill, North Carolina 27599

APOBEC3G (A3G) restricts HIV-1 infection by catalyzing processive C U deaminations on single-stranded DNA (ssDNA) with marked 3' 5' deamination polarity. Here we show that A3G exists in oligomeric states whose composition is dictated primarily by interactions with DNA, with salt playing an important, yet secondary, role. Directional deaminations correlate with the presence of dimers, tetramers, and larger oligomers observed by atomic force microscopy, and random deaminations appear to correlate mainly with monomers. The presence of a 30-nt weakly deaminated "dead" zone located at the 3'-ssDNA end implies the presence of a preferred asymmetric direction for A3G catalysis. Single turnover reaction rates reveal a salt-dependent inhibition of C deamination toward the 3'-ssDNA region, offering a molecular basis underlying A3G deamination polarity. Presteady state analysis demonstrates rapid diffusion-limited A3G-ssDNA binding, a slower salt-dependent conformational change, possibly indicative of DNA wrapping, and long (5–15 min) protein-DNA complex lifetimes. We suggest that diverse A3G oligomerization modes contribute to the human immunodeficiency virus, type 1, proviral DNA mutational bias.

Received for publication, February 7, 2008 , and in revised form, March 21, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grants ESO13192 and R37GM21422 (to M. F. G.) and Grant GM79480. This work was also supported by American Cancer Society Grant RSG-03-047 (to D. A. E.). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table S1 and Figs. S1–S6.

¹ To whom correspondence should be addressed: Dept. of Biological Sciences, Molecular and Computational Biology Section, 1050 Childs Way, Los Angeles, CA 90089. Fax: 213-821-1138; E-mail: mgoodman{at}usc.edu.

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