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Molecular and Cellular Biology, March 2004, p. 2352-2363, Vol. 24, No. 6
0270-7306/04/$08.00+0 DOI: 10.1128/MCB.24.6.2352-2363.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, United Kingdom
Received 1 October 2003/ Returned for modification 13 November 2003/ Accepted 19 December 2003
Childhood ataxia with central nervous system hypomyelination (CACH), or vanishing white matter leukoencephalopathy (VWM), is a fatal brain disorder caused by mutations in eukaryotic initiation factor 2B (eIF2B). eIF2B is essential for protein synthesis and regulates translation in response to cellular stresses. We performed mutagenesis to introduce changes equivalent to 12 human CACH/VWM mutations in three subunits of the equivalent factor from yeast (Saccharomyces cerevisiae) and analyzed effects on cell growth, translation, and gene expression in response to stresses. None of the mutations is lethal or temperature sensitive, but almost all confer some defect in eIF2B function significant enough to alter growth or gene expression under normal or stress conditions. Biochemical analyses indicate that mutations analyzed in eIF2B
and -
reduce the steady-state level of the affected subunit, while the most severe mutant tested, eIF2BßV341D (human eIF2BßV316D), forms complexes with reduced stability and lower eIF2B activity. eIF2B
is excluded from eIF2BßV341D complexes. eIF2Bßv341D function can be rescued by overexpression of eIF2B
alone. Our findings imply CACH/VWM mutations do not specifically impair responses to eIF2 phosphorylation, but instead cause protein structure defects that impair eIF2B activity. Altered protein folding is characteristic of other diseases, including cystic fibrosis and neurodegenerative disorders such as Huntington, Alzheimer's, and prion diseases.
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