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Murine leukemia virus maturation: protease region required for conversion from "immature" to "mature" core form and
Abstract:
Murine leukemia virus (MuLV) genome encodes a protease (Y. Yoshinaka, I. Katoh, T.D. Copeland, and S. Oroszlan (1985), Proc. Natl. Acad. Sci. USA 82, 1618-1622), which has been shown to cause maturation, specified as morphological conversion from "immature" to "mature" form of virus cores. To examine whether "immature" particles have infectivity or not, we constructed mutant DNAs with deletions in the protease region. The NIH/3T3 cells transfected with mutant DNAs produced "immature" particles, having immature morphology and containing Pr65gag, a polyprotein precursor of core proteins. The specific infectivity of the extracellularly released and purified particles was shown to be greatly reduced based on reverse transcriptase activity and protein content as compared with the "mature" particles obtained from wild-type DNA-transfected cells. The mutant genomes encoded functionally normal surface glycoprotein, gp70. These results strongly suggest that maturation of MuLV from "immature" to "mature" form of virus particles is indispensable to virus infectivity. The importance of processing of gag and pol, as well as transmembrane protein precursors by the viral protease is discussed.
Insights
Murine leukemia virus (MuLV) protease is essential for virus maturation and infectivity. Immature viral particles lacking protease activity show significantly reduced infectivity, highlighting the critical role of viral protease in the MuLV life cycle.
Area of Science:
- Virology
- Molecular Biology
- Biochemistry
Background:
- Murine leukemia virus (MuLV) possesses a protease responsible for viral maturation.
- Viral maturation involves morphological conversion from immature to mature virus cores.
- The role of immature particles in MuLV infectivity remains unclear.
Purpose of the Study:
- To investigate the infectivity of immature MuLV particles.
- To determine the necessity of viral protease for MuLV infectivity.
Main Methods:
- Construction of MuLV mutant DNAs with deletions in the protease region.
- Transfection of NIH/3T3 cells with mutant and wild-type DNAs.
- Production and purification of viral particles.
- Assessment of particle infectivity via reverse transcriptase activity and protein content.
- Analysis of viral glycoprotein (gp70) expression.
Main Results:
- Mutant DNAs produced immature MuLV particles containing Pr65gag.
- Immature particles exhibited significantly reduced specific infectivity compared to mature particles.
- Mutant genomes encoded functional surface glycoprotein gp70.
- Viral protease is crucial for processing gag and pol precursors.
Conclusions:
- MuLV particle maturation is indispensable for virus infectivity.
- The viral protease plays a critical role in MuLV replication by processing essential viral proteins.