Box 1, Figure I.

(a) A transmission electron micrograph of a section of a human cell expressing HIV-1 Gag and includes a single immature virus particle being released from the cell. (b) Gag is a multi-domain protein always containing, from N- to C-terminus, the MA domain (shown in green), the CA domain (blue), and the NC domain (red). Depending on the genus of retrovirus, one or a few additional domains or spacers may also be present. (c) The radial arrangement of Gag molecules that are in contact with membrane on the outside and RNA (yellow line) on the inside of the immature particle. There are on the order of 7 nucleotides per Gag molecule in the particle. Panel a is reproduced, with permission from [xxx].