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J. Virol., 10 1995, 6106-6114, Vol 69, No. 10
N Srinivasakumar, ML Hammarskjold and D Rekosh
The core of human immunodeficiency virus type 1 is derived from two
precursor polyproteins, Pr55gag and Pr160gag-pol. The Gag precursor can
assemble into immature virus-like particles when expressed by itself, while
the Gag-Pol precursor lacks particle-forming ability. We have shown
previously that the Gag precursor is able to "rescue" the Gag-Pol precursor
into virus-like particles when the two polyproteins are expressed in the
same cell by using separate simian virus 40-based plasmid expression
vectors. To understand this interaction in greater detail, we have made
deletion mutations in the capsid-coding regions of Gag- and
Gag-Pol-expressing plasmids and assayed for the abilities of these
precursors to assemble into virus-like particles. When we tested the
abilities of Gag-Pol precursors to be incorporated into particles of Gag by
coexpressing the precursors, we found that mutant Gag-Pol precursors
lacking a conserved region in retroviral capsid proteins, the major
homology region (MHR), were excluded from wild-type Gag particles. Mutant
precursors lacking MHR were also less efficient in processing the Gag
precursor in trans. These results suggest that the MHR is critical for
interactions between Gag and Gag-Pol molecules. In contrast to these
results, expression of mutated Gag precursors alone showed that deletions
in the capsid region, including those which removed the MHR, reduced the
efficiency of particle formation by only 40 to 50%. The mutant particles,
however, were clearly lighter than the wild type in sucrose density
gradients. These results indicate that the requirements for Gag particle
formation differ from the ones essential for efficient incorporation of the
Gag-Pol precursor into these particles.
Copyright © 1995, American Society for Microbiology
Characterization of deletion mutations in the capsid region of human immunodeficiency virus type 1 that affect particle formation and Gag- Pol precursor incorporation
Myles H. Thaler Center for AIDS and Human Retrovirus Research, University of Virginia, Charlottesville 22908, USA.
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