Fig. 5.

Nucleocapsid maturation Gag processing is sequential and ordered. The first PR to be self-processed from Gag-Pol is thought to direct the sequential Gag and Gag-Pol proteolytic events that will ultimately convert the immature virion into the mature particle (a–e). PR self-activation and cleavage from Gag-Pol is driven by the proper alignment of HIV-1 Gag-Pol precursors within the immature particle. The different protein species generated during the steps of Gag processing are indicated. PR cleavage of Gag initially occurs between SP1 and NC leading to the first NC intermediate form, NCp15 (partial cleavage product containing NC/SP2/p6), cleavage then results in NCp9 (partial cleavage product containing NC/SP2), and finally to the fully processed form, NCp7. The self-assembly properties of CA and NC, after removal of SP1, SP2 and p6, allow assembly of the viral core. Furthermore, SP1-NC cleavage by PR separates the MA-CA from the nucleocapsid complex formed between RNA, NCp15, RT, and IN. Processing of NCp15 by PR into NCp9 leads to a NC/RNA condensed aggregate, in which NCp9 is finally processed into NCp7, allowing the reverse transcription complex to form and be primed for function within the confines of the capsid cone