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M9640640.TXT
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1996-03-04
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Document 0640
DOCN M9640640
TI The human immunodeficiency virus type 1 5' packaging signal structure
affects translation but does not function as an internal ribosome entry
site structure.
DT 9604
AU Miele G; Mouland A; Harrison GP; Cohen E; Lever AM; University of
Cambridge Department of Medicine, Addenbrooke's; Hospital, United
Kingdom.
SO J Virol. 1996 Feb;70(2):944-51. Unique Identifier : AIDSLINE
MED/96135205
AB The role of the RNA secondary structure in the 5' packaging signal
region of human immunodeficiency virus type 1 (HIV-1) in initiating
translation of gag mRNA has been investigated both in vitro and in the
presence of cellular cofactors in vivo. Heat denaturation of the
structure and mutagenic deletion both lead to an increase in levels of
translated products, indicating that the structure is a significant
inhibitor of translation. The proximity of the gag AUG to the packaging
signal structure suggested that it might function as an internal
ribosome entry site. However, in both a cell-free system and eukaryotic
cells, translation will initiate at a novel upstream initiation codon
introduced within the 5' noncoding region. This codon is utilized
exclusively, resulting in gag protein products with an extra 11 amino
acids at the amino terminus, which, when expressed in T lymphocytes, are
confined intracellularly, probably because of the lack of an N-terminal
glycine myristoylation signal. Deletion of the secondary structure
abolishes gag production even in the presence of tat and rev in trans.
Using dicistronic constructs containing the HIV-1 5' leader cloned
between two heterologous open reading frames, we were unable to detect
any significant expression of the second open reading frame that would
have been supportive of an internal ribosome entry site mechanism. Using
mutant proviruses either lacking the entire packaging signal structure
region or containing the introduced upstream initiation codon in
long-term replication studies, we were unable to detect reverse
transcriptase activity in culture supernatants. The 5' packaging signal
structure of HIV-1 does not serve as an internal ribosome entry site.
The translation of gag is consistent with ribosomal scanning. However,
the packaging signal structure causes significant translational
inhibition.
DE Amino Acid Sequence Animal Base Sequence Cell Line Codon, Initiator
Fusion Proteins, gag-pol/*GENETICS Hela Cells Human
HIV-1/*GENETICS/PHYSIOLOGY Molecular Sequence Data *Nucleic Acid
Conformation Peptide Chain Initiation/*PHYSIOLOGY Reticulocytes
Ribosomes/*METABOLISM RNA, Messenger/CHEMISTRY/*GENETICS RNA,
Viral/CHEMISTRY/*GENETICS Structure-Activity Relationship Support,
Non-U.S. Gov't Transcription, Genetic Virus Assembly JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).