Figure 1.

Illustration showing retroviral genome packaging events. The retroviral genomic RNA is exported from the nucleus to cytoplasm and used as the mRNA for ribosomal synthesis of the Gag and Gag–Pol polyproteins. (A) The retroviral genomic RNA promotes conversion of the dimeric form of genomic RNA via the NC domain of Gag. (B) The Gag and retroviral genomic RNA complex is transported to the plasma membrane, where further assembly and budding occur, mediated by the myristoylated MA domain of Gag. (C) In contrast, spliced viral RNA or cellular RNA is not bound to the NC domain of Gag or may be bound to a small number of Gag polyproteins insufficient for trafficking to the plasma membrane.