Figure 2.

Selection of genomic RNA from non-genomic viral RNA. Dotted lines signify splicing or production of sub-genomic RNA. (a) Non-genomic RNA cannot be packaged because it does not contain the high affinity binding site for the (nucleo)capsid protein; (b) Non-genomic RNA contains the sequences for high affinity binding site, but it is not presented for binding. In HIV-1, negative regulatory elements (−ve) upstream of the splice donor (SD) conceal the Gag binding site unless counteracted by positive regulatory (+ve) sequences downstream of the SD.