POSITIONALLY INDEPENDENT AND EXCHANGEABLE LATE BUDDING FUNCTIONS OF THE ROUS-SARCOMA VIRUS AND HUMAN-IMMUNODEFICIENCY-VIRUS GAG PROTEINS

The Gag proteins of Rous sarcoma virus and human immunodeficiency viru s (HIV) each contain a function involved in a late step in budding, de fects in which result in the accumulation of these molecules at the pl asma membrane. In the Rous sarcoma virus Gag protein (pr76(gag)), this assembly domain is associated with a PPPY motif, which is located at an internal position between the MA and CA sequences. This motif is no t contained anywhere within the HIV Gag protein (pr55(gag)), and the M A sequence is linked directly to CA. Instead, a late assembly function of HIV has been associated with the p6 sequence situated at the C ter minus of Gag. Here we demonstrate the remarkable finding that the late assembly domains from these two unrelated Gag proteins are exchangeab le between retroviruses and can function in a positionally independent manner.