Human immunodeficiency virus (HIV) is the causing agent of the acquired immune deficiency syndrome (AIDS). Like all retroviruses, HIV carries two copies of viral genomic RNA in each virion. HIV genome encodes three structural genes, including gag, pol and env, as well as two regulatory genes (rev and tat) and four accessory genes (vif, vpr, vpu and nef). It is noted that none of these nine viral proteins bears the helicase activity. Helicases are able to unwind RNA duplex and remodel the structure of RNA-protein (RNP) complexes using energy derived from hydrolysis of nucleotide triphosphates (NTPs). They are involved in every step of cellular RNA metabolisms. It is conceivable that HIV needs to exploit cellular RNA helicases to promote the replication of its RNA at various steps such as transcription, folding and transport. / In this study, we found that a DEAD-box protein named DDX24 associates with HIV-1 Gag in an RNA-dependent manner but is not found within virus particles. Knockdown of DDX24 inhibits the packaging of HIV-1 RNA and thus diminishes viral infectivity. The decreased viral RNA packaging as a result of DDX24-knockdown is observed only in the context of the Rev/RRE (Rev response element)-dependent but not the CTE (constitutive transport element)-mediated nuclear export of viral RNA, which is explained by the specific interaction of DDX24 with the Rev protein. We propose that DDX24 acts at the early phase of HIV-1 RNA metabolism prior to nuclear export and the consequence of this action extends to the viral RNA packaging stage during virus assembly.

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