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J. Virol., Aug 1996, 5548-5556, Vol 70, No. 8
GV Merkulov, KM Swiderek, CB Brachmann and JD Boeke
Cleavage of the Gag and Gag-Pol polyprotein precursors is a critical step
in proliferation of retroviruses and retroelements. The Ty1 retroelement of
Saccharomyces cerevisiae forms virus-like particles (VLPs) made of the Gag
protein. Ty1 Gag is not obviously homologous to the Gag proteins of
retroviruses. The apparent molecular mass of Gag is reduced from 58 to 54
kDa during particle maturation. Antibodies raised against the C-terminal
peptide of Gag react with the 58-kDa polypeptide but not with the 54-kDa
one, indicating that Gag is proteolytically processed at the C terminus. A
protease cleavage site between positions 401 and 402 of the Gag precursor
was defined by carboxy-terminal sequencing of the processed form of Gag.
Certain deletion and substitution mutations in the C terminus of the Gag
precursor result in particles that are two-thirds the diameter of the
wild-type VLPs. While the Ty1 protease is active in these mutants, their
transposition rates are decreased 20-fold compared with that of wild-type
Ty1. Thus, the Gag C-terminal portion, released in the course of particle
maturation, probably plays a significant role in VLP morphogenesis and Ty1
transposition.
Copyright © 1996, American Society for Microbiology
A critical proteolytic cleavage site near the C terminus of the yeast retrotransposon Ty1 Gag protein
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21025, USA.
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