       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).

