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The N-terminal 31 amino acids of human immunodeficiency virus type 1 envelope protein gp120 contain a potential gp41 contact site

We have compared the expression of full-length gp160 envelope protein from human immunodeficiency virus type 1 with that of a deletion mutant lacking the N-terminal 31 amino acids of the mature protein (gp160 delta 32). The gp160 and gp160 delta 32 proteins are processed to yield gp41 and gp120 or gp120 delta 32, respectively. In contrast to full-length gp120, gp120 delta 32 failed to associate with gp41 at the cell surface, despite conformational integrity as judged by soluble CD4 binding. Thus, the N-terminal 31 amino acids of gp120, which contain hyperconserved sequences, are likely involved in forming a contact site for gp41.