Roles of Gag and NCp7 in Facilitating [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} Annealing to Viral RNA in Human Immunodeficiency Virus Type 1

In protease-negative human immunodeficiency virus type 1 (HIV-1) [Pr(-)], the amount of [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealed by Gag is modestly reduced (∼25%) compared to that annealed by mature nucleocapsid (NCp7) in protease-positive HIV-1 [Pr(+)]. However, the [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealed by Gag also has a strongly reduced ability to initiate reverse transcription and binds less tightly to viral RNA. Both in vivo and in vitro, APOBEC3G (A3G) inhibits [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealing facilitated by NCp7 but not annealing facilitated by Gag. While transient exposure of Pr(-) viral RNA to NCp7 in vitro returns the quality and quantity of [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealing to Pr(+) levels, the presence of A3G both prevents this rescue and creates a further reduction in [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealing. Since A3G inhibition of NCp7-facilitated [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealing in vitro requires the presence of A3G during the annealing process, these results suggest that in Pr(+) viruses NCp7 can displace Gag-annealed [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} and re-anneal it to viral RNA, the re-annealing step being subject to A3G inhibition. This supports the possibility that the initial annealing of [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} in wild-type, Pr(+) virus may be by Gag and not by NCp7, perhaps offering the advantage of Gag's preference for binding to RNA stem-loops in the 5′ region of viral RNA near the [fleqn,10pt,legalpaper]{article} {amssymb} {amsfonts} {amsmath} {empty} {document} \(tRNA₃Lys\) {document} annealing region.