Env in HIV
The env gene does not actually code for gp120 and gp41, but for a precursor to both, gp160. During HIV reproduction, the host cell's own enzymes cleave gp160 into gp120 and gp41. The host cell protease that cleaves Env into gp120 and gp41 is Furin. See Replication cycle of HIV.
Env expression is regulated by the gene product of rev. Experimental deletion of rev resulted in the inability to detect the Env protein and levels of env mRNA in the cell cytoplasm were significantly diminished. However, when total cellular RNA was analyzed, env RNA totals were not significantly difference in the presence and absence of rev coexpression. It was found that without rev expression, there was a marked increase in nuclear env RNA, which suggests that rev plays an important role in the nuclear export of env mRNA. The role of rev was further elucidated when it was found that Rev acts in trans to target a specific sequence present in the env gene of HIV-1 to initiate export of incompletely spliced HIV-1 RNA from the nucleus.
Read more about this topic: Env (gene)