Analysis of a human immunodeficiency virus type 1 gag mutant with an engineered 110-amino-acid insertion in the matrix protein domain

Abstract

A human immunodeficiency virus (HIV) matrix (MA) protein mutant was constructed by duplication of 107 codons of the HIV-1 MA domain. This MA protein duplication mutant (MAII) still could assemble and process particles, had a wild-type (wt) HIV particle density, and possessed reverse transcriptase activity of about 80% of the wild type virus level. The incorporation of HIV Env and viral RNA genome was not greatly affected. The MAII was noninfectious or poorly infectious, however, when pseudotyped with an amphotropic murine leukemia virus envelope protein or with the HIV envelope protein. Although the MAII mutant displayed an immunofluorescence staining pattern similar to that of the wild type virus, subcellular fractionation studies indicated that the membrane association of MAII Gag precursors was unstable under high-salt conditions. Electron microscopic studies showed that the mutant had a decreased density of particle cores compared with that of the wild type virus, suggesting an altered arrangement of the packed proteins. As this insertion in the MA gene caused no major effects on virus assembly implies that the HIV-1 gag has the potential to adapt large insertions of extra coding sequences without loss of the ability to direct particle assembly and release.