The Major Human Immunodeficiency Virus Type 2 (HIV-2) Packaging Signal Is Present on All HIV-2 RNA Species: Cotranslational RNA Encapsidation and Limitation of Gag Protein Confer Specificity

Deletion of a region of the human immunodeficiency virus type 2 (HIV-2) 5′ leader RNA reduces genomic RNA encapsidation to about 5% that of wild-type virus with no defect in viral protein production but severely limits virus spread in Jurkat T cells, indicating that this region contains a major cis-acting encapsidation signal, or psi (Ψ). Being upstream of the major splice donor, it is present on all viral transcripts. We have shown that HIV-2 selects its genomic RNA for encapsidation cotranslationally, rendering wild-type HIV-2 unable to encapsidate vector RNAs in trans . Virus with Ψ deleted, however, encapsidates an HIV-2 vector, demonstrating competition for Gag protein. HIV-2 overcomes the lack of packaging signal location specificity by two novel mechanisms, cotranslational packaging and competition for limiting Gag polyprotein.