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Journal of Virology, September 2000, p. 8709-8719, Vol. 74, No. 18
Department of Microbiology, Immunology and Molecular
Genetics, Molecular Biology Institute, Johnsson Comprehensive
Cancer Center, UCLA School of Medicine, Los Angeles, California
90095-1747,1 and Institut für
Immunologie und Molekularbiologie, Fachbereich Veterinärmedizin
der Freien Universität Berlin, D-10117 Berlin,
Germany2
Received 22 February 2000/Accepted 8 June 2000
Influenza virus matrix protein (M1), a critical protein required
for virus assembly and budding, is presumed to interact with viral
glycoproteins on the outer side and viral ribonucleoprotein on the
inner side. However, because of the inherent membrane-binding ability
of M1 protein, it has been difficult to demonstrate the specific
interaction of M1 protein with hemagglutinin (HA) or neuraminidase
(NA), the influenza virus envelope glycoproteins. Using Triton X-100
(TX-100) detergent treatment of membrane fractions and floatation in
sucrose gradients, we observed that the membrane-bound M1 protein
expressed alone or coexpressed with heterologous Sendai virus F was
totally TX-100 soluble but the membrane-bound M1 protein expressed in
the presence of HA and NA was predominantly detergent resistant and
floated to the top of the density gradient. Furthermore, both the
cytoplasmic tail and the transmembrane domain of HA facilitated binding
of M1 to detergent-resistant membranes. Analysis of the membrane
association of M1 in the early and late phases of the influenza virus
infectious cycle revealed that the interaction of M1 with mature
glycoproteins which associated with the detergent-resistant lipid rafts
was responsible for the detergent resistance of membrane-bound M1.
Immunofluorescence analysis by confocal microscopy also demonstrated that, in influenza virus-infected cells, a fraction of M1 protein colocalized with HA and associated with the HA in transit to the plasma
membrane via the exocytic pathway. Similar results for colocalization
were obtained when M1 and HA were coexpressed and HA transport was
blocked by monensin treatment. These studies indicate that both HA and
NA interact with influenza virus M1 and that HA associates with M1 via
its cytoplasmic tail and transmembrane domain.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Influenza Virus Assembly: Effect of Influenza Virus Glycoproteins
on the Membrane Association of M1 Protein
*
Corresponding author. Mailing address: Department of
Microbiology, Immunology and Molecular Genetics, Molecular Biology
Institute, Johnsson Comprehensive Cancer Center, UCLA School of
Medicine, Los Angeles, CA 90095-1747. Phone: (310) 825-8558. Fax: (310) 206-3865. E-mail: dnayak{at}ucla.edu.
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