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J. Biol. Chem., Vol. 280, Issue 17, 17488-17496, April 29, 2005

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A HIV-1 Minimal Gag Protein Is Superior to Nucleocapsid at in Vitro Annealing and Exhibits Multimerization-induced Inhibition of Reverse Transcription^*

Ariel Roldan, Otis U. Warren, Rodney S. Russell¶, Chen Liang||, and Mark A. Wainberg¶||**

From the McGill University AIDS Centre, Lady Davis Institute-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada and the ^¶Department of Microbiology and Immunology and ^||Division of Experimental Medicine, McGill University, Montreal, Quebec H3A 2B4, Canada

HIV-1 uses to prime reverse transcription of its viral RNA. In this process, the 3'-end of must be annealed to the primer binding site of HIV-1 genomic RNA, and the two molecules together form a complex structure. During annealing, the nucleocapsid (NC) protein enhances the unwinding of tertiary structures within both RNA molecules. Moreover, the packaging of occurs prior to viral budding at a time when NC is still part of the Pr55^Gag polyprotein. In contrast, Pr55^Gag is able to produce virus-like particles on its own. We have recently shown that an N-terminal extended form of NC (mGag), containing all of the minimal elements required for virus-like particle formation, possesses greater affinity for HIV-1 genomic RNA than does NC alone. We have now studied the -annealing properties of mGag in comparison to those of NC and report that the former is more efficient in this regard than the latter. We have also tested each of a mutant version of mGag, an extended form of mGag, and an almost full-length form of Gag, and showed that all of these possessed greater tRNA-annealing capacity than did the viral NC protein. Yet, surprisingly, multimerization of Gag-related proteins did not abrogate this annealing process but rather resulted in dramatically reduced levels of reverse transcriptase processivity. These results suggest that the initial stages of reverse transcription may be regulated by the multimerization of Pr55^Gag polyprotein at times prior to the cleavage of NC.

Received for publication, February 3, 2005 , and in revised form, February 22, 2005.

^* This research was supported by the Canadian Institutes of Health Research. 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.

Work performed was in fulfillment of the year-out "Scholarly Pursuit" requirement toward a Doctorate of Medicine degree at the University of Pennsylvania.

^** To whom correspondence should be addressed: McGill AIDS Centre, Lady Davis Institute-Jewish General Hospital, 3755 Cote Ste-Catherine, Montreal, Quebec H3T 1E2, Canada. Tel.: 514-340-8260; Fax: 514-340-7537; E-mail: mark.wainberg{at}mcgill.ca.

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