The genome of retroviruses contains three major coding regions for virion proteins, gag, pol and env. Gag encompasses information for nonglycosylated viral proteins that form the matrix, the capsid and the nucleoprotein structures. From pol derive reverse transcriptase and integrase, and env codes for the surface glycoproteins of the virion which consist of a transmembrane and a surface domain, linked by disulfide bonds. A viral protease is derived eitherfrom the gagorfrom the pol coding region, depending on the virus. Simple retroviruses contain only this elementary gag, pol, and env coding...