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Assessment of Selective mRNA Translation in Mammalian Cells by Polysome Profiling
10:00

Assessment of Selective mRNA Translation in Mammalian Cells by Polysome Profiling

Published on: October 28, 2014

Cap-independent polysomal association of natural mRNAs encoding c-myc, BiP, and eIF4G conferred by internal ribosome

G Johannes1, P Sarnow

  • 1Department of Microbiology and Immunology, Stanford University School of Medicine, California 94305, USA.

RNA (New York, N.Y.)
|December 16, 1998
PubMed

Insights

Internal ribosome entry sites (IRES) function in natural cellular mRNAs, even when cap-dependent translation is blocked. This allows synthesis of essential proteins like eIF4G during viral infections.

Area of Science:

  • Molecular Biology
  • Virology
  • Gene Expression

Background:

  • Internal ribosome entry sites (IRES) are known in viral and some cellular mRNAs.
  • Their function within natural, capped cellular mRNAs, especially during stress, is less understood.

Purpose of the Study:

  • To investigate the functionality of IRES elements in their native capped cellular mRNAs.
  • To determine if IRES-mediated translation persists when cap-dependent translation is inhibited.

Main Methods:

  • Polysomal association and translation assays were performed on IRES-containing cellular mRNAs.
  • Experiments were conducted in cells infected with poliovirus to inhibit cap-dependent translation.
  • cDNA expression library screening was used to isolate and test eIF4GI mRNA sequences.

Main Results:

  • Several known IRES-containing mRNAs (e.g., BiP, c-myc) remained associated with the translation apparatus and were translated during poliovirus infection.
  • eIF4GI and eIF4GII mRNAs were also found in polysomes in infected cells.
  • The 5'-end of eIF4GI mRNA demonstrated IRES activity in a dicistronic mRNA assay.

Conclusions:

  • IRES elements are functional in their natural capped cellular mRNAs, even under conditions that block cap-dependent translation.
  • eIF4G proteins can be synthesized via IRES-mediated translation during viral infections.
  • This suggests a role for eIF4G in both cap-dependent and cap-independent translation initiation.

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