HIV-1 protease autoprocessing is responsible for liberation of free mature protease (PR) from the Gag-Pol polyprotein precursor. A cell-based model system was previously developed to examine the autoprocessing mechanism of fusion precursors carrying the p6*-PR miniprecursor sandwiched between various proteins or epitopes. We here report that precursor autoprocessing is context-dependent as its activity and outcomes can be modulated by sequences upstream of p6*-PR. This was exemplified by the 26aa maltose binding protein (MBP) signal peptide (SigP) when placed at the N-terminus of a fusion precursor. The mature PRs released from SigP-carrying precursors are resistant to self-degradation whereas those released from SigP-lacking fusion precursors are prone to self-degradation. A H69D mutation in PR abolished autoprocessing of SigP-containing fusion precursors whereas it only partially suppressed autoprocessing of fusion precursors lacking SigP. An autoprocessing deficient GFP fusion precursor with SigP exhibited a subcellular distribution pattern distinct from the one without it in transfected HeLa cells. Furthermore, a SigP fusion precursor carrying a substitution at the P1 position released the mature PR and PR-containing fragments that were different from those released from the precursor carrying the same mutation but lacking SigP. We also examined autoprocessing outcomes in viral particles produced by a NL4-3 derived proviral construct and demonstrated the existence of several PR-containing fragments along with the mature PR. Some of these resembled the SigP precursor autoprocessing outcomes. This finding of context-dependent modulation reveals the complexity of precursor autoprocessing regulation that most likely accompanies sequence variation imposed by the evolution of the upstream Gag moiety.

HIV-1蛋白酶的自动加工负责从Gag-Pol多蛋白前体中释放出游离的成熟蛋白酶（PR）。以前已经开发出了基于细胞的模型系统，以研究携带p6 * -PR微型前体夹在各种蛋白质或表位之间的融合前体的自动加工机制。我们在这里报告前体自动加工是上下文相关的，因为其活性和结果可以通过p6 * -PR上游的序列进行调节。当置于融合前体的N末端时，26aa麦芽糖结合蛋白（MBP）信号肽（SigP）就是例证。从携带SigP的前体释放的成熟PR能够抵抗自降解，而从缺乏SigP的融合前体释放的PR则易于自我降解。PR中的H69D突变废除了含有SigP的融合前体的自动加工，而仅部分抑制了缺乏SigP的融合前体的自动加工。具有SigP的自动加工缺陷GFP融合前体在转染的HeLa细胞中表现出不同于没有它的亚细胞分布模式。此外，在P1位置带有取代基的SigP融合前体释放出成熟的PR和含PR的片段，该片段不同于从具有相同突变但缺少SigP的前体中释放的片段。我们还检查了由NL4-3衍生的前病毒构建体产生的病毒颗粒中的自动加工结果，并证明了几个PR片段以及成熟PR的存在。其中一些类似于SigP前体的自动处理结果。