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M9630086.TXT
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1996-02-27
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Document 0086
DOCN M9630086
TI The retrotransposon Tf1 assembles virus-like particles that contain
excess Gag relative to integrase because of a regulated degradation
process.
DT 9603
AU Atwood A; Lin JH; Levin HL; Laboratory of Molecular Genetics, National
Institutes of Child; Health and Human Development, Bethesda, Maryland
20892, USA.
SO Mol Cell Biol. 1996 Jan;16(1):338-46. Unique Identifier : AIDSLINE
MED/96104584
AB The retrotransposon Tf1, isolated from Schizosaccharomyces pombe,
contains a single open reading frame with sequences encoding Gag,
protease, reverse transcriptase, and integrase (IN). Tf1 has previously
been shown to possess significant transposition activity. Although Tf1
proteins do assemble into virus-like particles, the assembly does not
require readthrough of a translational reading frame shift or stop
codon, common mechanisms used by retroelements to express Gag in molar
excess of the polymerase proteins. This study was designed to determine
if Tf1 particles contain equal amounts of Gag and polymerase proteins or
whether they contain the typical molar excess of Gag. After using two
separate methods to calibrate the strength of our antibodies, we found
that both S. pombe extracts and partially purified Tf1 particles
contained a 26-fold molar excess of Gag relative to IN. Knowing that Gag
and IN are derived from the same Tf1 primary translation product, we
concluded that the excess Gag most likely resulted from specific
degradation of IN. We obtained evidence of regulated IN degradation in
comparisons of Tf1 protein extracted from log-phase cells and that
extracted from stationary-phase cells. The log-phase cells contained
equal molar amounts of Gag and IN, whereas cells approaching stationary
phase rapidly degraded IN, leaving an excess of Gag. Analysis of the
reverse transcripts indicated that the bulk of reverse transcription
occurred within the particles that possess a molar excess of Gag.
DE Base Sequence DNA Nucleotidyltransferases/*GENETICS/METABOLISM DNA
Primers/GENETICS DNA, Fungal/GENETICS Gene Products,
gag/*GENETICS/METABOLISM Molecular Sequence Data Protein Processing,
Post-Translational *Retrotransposons Retroviridae/GROWTH &
DEVELOPMENT/GENETICS/METABOLISM
Schizosaccharomyces/*GENETICS/METABOLISM/*VIROLOGY JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).