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Journal of Virology, December 2002, p. 12712-12722, Vol. 76, No. 24
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.24.12712-12722.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Novel Mutations That Control the Sphingolipid and Cholesterol Dependence of the Semliki Forest Virus Fusion Protein
Prodyot K. Chatterjee, Christina H. Eng,
and Margaret Kielian*
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461
Received 19 June 2002/
Accepted 16 September 2002
The enveloped alphavirus Semliki Forest virus (SFV) infects cells via a membrane fusion reaction mediated by the E1 membrane protein. Efficient SFV-membrane fusion requires the presence of cholesterol and sphingolipid in the target membrane. Here we report on two mutants, srf-4 and srf-5, selected for growth in cholesterol-depleted cells. Like the previously isolated srf-3 mutant (E1 proline 226 to serine), the phenotypes of the srf-4 and srf-5 mutants were conferred by single-amino-acid changes in the E1 protein: leucine 44 to phenylalanine and valine 178 to alanine, respectively. Like srf-3, srf-4 and srf-5 show striking increases in the cholesterol independence of growth, infection, membrane fusion, and exit. Unexpectedly, and unlike srf-3, srf-4 and srf-5 showed highly efficient fusion with sphingolipid-free membranes in both lipid- and content-mixing assays. Both srf-4 and srf-5 formed E1 homotrimers of decreased stability compared to the homotrimers of the wild type and the srf-3 mutant. All three srf mutations lie in the same domain of E1, but the srf-4 and srf-5 mutations are spatially separated from srf-3. When expressed together, the three mutations could interact to produce increased sterol independence and to cause temperature-sensitive E1 transport. Thus, the srf-4 and srf-5 mutations identify novel regions of E1 that are distinct from the fusion peptide and srf-3 region and modulate the requirements for both sphingolipid and cholesterol in virus-membrane fusion.
* Corresponding author. Mailing address: Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-3638. Fax: (718) 430-8574. E-mail:
kielian{at}aecom.yu.edu.
Present address: The Integrated Program in Cellular, Molecular and Biophysical Studies, College of Physicians and Surgeons, Columbia University, New York, NY 10032.
Journal of Virology, December 2002, p. 12712-12722, Vol. 76, No. 24
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.24.12712-12722.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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