Human foamy virus
the case of HTLV and HIV, a range of differently spliced mRNAs encode various regulatory proteins. All the mRNAs share a common sequence at their 5' end. The viral protease is responsible for posttranslational cleavage of the Gag polyprotein to yield the matrix, capsid, and nucleocapsid proteins, and also for cleavage of the Pol polyprotein to yield the reverse transcrip-tase/RNase H and the integrase. On the other hand, the Env polyprotein is cleaved by a cellular protease to yield two envelope glycoproteins: a transmembrane protein and a receptor-binding protein.
The details of assembly of the virion are not fully understood and differ from genus to genus. Two covalently linked molecules of the full-length plus sense genomic RNA assemble into a core structure by interaction of a packaging signal in the leader sequence of the RNA with a zinc-finger motif in the nucleocapsid protein. Capsids generally assemble at the cell surface. Myristy-lated and glycosylated envelope proteins enter the plasma membrane and form the peplomers of the envelope which the virion gains by exocytosis. The final proteolytic cleavage steps occur during and even after budding.
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