Deletion mutagenesis within the dimerization initiation site of human immunodeficiency virus type 1 results in delayed processing of the p2 peptide from precursor proteins

Previous work has shown that deletions of genomic segments at nucleotide (n t) positions +238 to +253, i.e., construct BH10-LD3, or nt positions +261 t o +274, i.e., construct BH10-LD4, within the human immunodeficiency virus t ype 1 (HIV-1) dimerization initiation site (DIS) destroyed DIS secondary st ructure and dramatically reduced viral replication capacity. Surprisingly, two point mutations located within the viral peptide 2 (p2) and nucleocapsi d (NC) protein termed MP2 and MNC, respectively, were able to compensate fo r this defect. Since the MP2 mutation involves an amino acid substitution n ear the cleavage site between p2 and NC, we investigated the effects of the above-mentioned deletions on the processing of Gag proteins. Immunoprecipi tation assays performed with monoclonal antibodies against viral capsid (CA ) (p24) protein showed that p2 was cleaved from CA with less efficiency in viruses that contained the LD3 and LD4 deletions than in wild-type viruses. The presence of the two compensatory mutations, MP2 and MNC, increased the efficiency of the cleavage of p2 from CA, but neither mutation alone had t his effect or was sufficient to compensate for the observed impairment in i nfectiousness. A virus that contained both of the above-mentioned deletions within the DIS was also impaired in regard to processing and infectiousnes s, and it could likewise be compensated by the MP2 and MNC point mutations. These results suggest that the DIS region of HIV-1 RNA plays an important role in the processing of Gag proteins.