NOVEL GAG-POL FRAMESHIFT SITE IN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 VARIANTS RESISTANT TO PROTEASE INHIBITORS

Human immunodeficiency virus type 1 (HIV-1) variants resistant to prot ease inhibitors have been shown to contain a mutation in the p1/p6 Gag precursor cleavage site, At the messenger RNA level, this mutation ge nerates a U UUU UUU sequence that is reminiscent of the U UUU UUA sequ ence required for ribosomal frameshifting and Gag-Pol synthesis. To te st whether the p1/p6 cleavage site mutation was generating a novel fra meshift site, HIV sequences were inserted in translation vectors conta ining a chloramphenicol acetyltransferase (CAT) reporter gene requirin g -1 frameshifting for expression. All sequences containing the origin al HIV frameshift site supported the synthesis of CAT but expression w as increased 3- to Il fold in the presence of the mutant p1/p6 sequenc e. When the original frameshift site was abolished by mutation, expres sion remained unchanged when using constructs containing the mutant p1 /p6 sequence, whereas it was decreased 2- to 4.5-fold when using wild- type p1/p6 constructs. Similarly, when introduced into HIV molecular c lones, the p1/p6 mutant sequence supported Gag-Pol synthesis and prote ase activity in the absence of the original frameshift site, indicatin g that this sequence could also promote ribosomal frameshifting in vir us-expressing cells.