Assembly and release of human immunodeficiency virus type 1 Gag proteins containing tandem repeats of the matrix protein coding sequences in the matrix domain

We have constructed human immunodeficiency virus (HIV) gag mutants by incre asing the matrix protein (MA) sequences via tandemly repeated duplication o f the central 107-MA codons. Instead of a total of 132 amino acid residues for the wild-type MA, the resultant mutants designated as MA2, MA3, and MA4 contained a total of 242, 352, and 462 codons in the MA domains, respectiv ely. Analysis indicated that the addition of 110 or 220 amino acid residues to the MA did not significantly affect the assembly, release, and processi ng of particles; however, particle production was markedly reduced when ano ther copy of 110 residues was added to the MA. Subcellular fractionation an alysis suggested that the MA tandem repeat mutations enhanced the Gag membr ane affinity, in a manner which correlated with the copy number of MA seque nces. The effects of enhanced membrane affinity were substantially reduced when sequences downstream of the capsid (CA) domain were deleted. Sucrose d ensity gradient fractionation analysis showed that particles produced by th e large insertion mutants possessed wild-type (wt) HIV particle density. Tr uncation of sequences downstream of the nucleocapsid (NC) domains of the mu tants did not influence the budding of particles. In contrast, particle bud ding was severely impaired when sequences downstream of the CA domain were truncated. Particle densities for the large Gag proteins, which were trunca ted at the C-terminus of CA, were about 1.12-1.14 g/ml lower than that for wt. Our results suggest that the HIV MA domain could adopt insertions of la rge protein sequences, and strongly support the proposal that the NC and p2 domains play a crucial role in the process of correct Gag protein packing. (C) 2000 Academic Press.