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J. Virol., Jun 1996, 3440-3448, Vol 70, No. 6
KJ Orlinsky, J Gu, M Hoyt, S Sandmeyer and TM Menees
The Saccharomyces cerevisiae retroviruslike element Ty3 encodes the major
structural proteins capsid (CA) and nucleocapsid in the GAG3 open reading
frame. The Ty3 CA protein contains a sequence (QGX2EX5FX3LX3H, where H is a
hydrophobic residue) which has not been observed in other retrotransposons
but which is similar to the major homology region (MHR) described for
retrovirus CA. In this study the effects of mutations in the Ty3 MHR on
particle formation, processing, DNA synthesis, and transposition were
examined. Each of the mutations tested resulted in severe defects in
transposition, with disruption occurring prior to or at particle formation,
subsequent to particle formation and prior to completion of DNA synthesis,
and subsequent to DNA synthesis. Changing the Q in the motif to R had
relatively little effect on particle formation but decreased transposition
to about 13% of that of a wild-type element. Changing G to A or V almost
completely eliminated the formation of intracellular particles, possibly by
disruption of CA-CA interactions. Changes introduced at the position of E
resulted in blocked processing, blocked DNA synthesis, or a block at some
post-reverse transcription step, depending on the nature of the mutation
introduced. These results showed that the integrity of the Ty3 MHR is
required for multiple aspects of Ty3 replication involving CA. These
functions are independent of extracellular budding and of infection,
aspects of the retroviral life cycle which are not recapitulated in
replication of the Ty3 retrotransposon.
Copyright © 1996, American Society for Microbiology
Mutations in the Ty3 major homology region affect multiple steps in Ty3 retrotransposition
Department of Microbiology and Genetics, University of California, Irvine, 92717, USA.
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