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J Virol, May 1998, p. 3554-3559, Vol. 72, No. 5
Institut für Virologie,
Philipps-Universität Marburg, 35011 Marburg, Germany
Received 17 November 1997/Accepted 21 January 1998
The hemagglutinin (HA) of fowl plague virus was lengthened and
shortened by site-specific mutagenesis at the cytoplasmic tail, and the
effects of these modifications on HA functions were analyzed after
expression from a simian virus 40 vector. Elongation of the tail by the
addition of one to six histidine (His) residues did not interfere with
intracellular transport, glycosylation, proteolytic cleavage,
acylation, cell surface expression, and hemadsorption. However, the
ability to induce syncytia at a low pH decreased dramatically depending
on the number of His residues added. Partial fusion (hemifusion),
assayed by fluorescence transfer from octadecylrhodamine-labeled
erythrocyte membranes, was also reduced, but even with the mutant
carrying six His residues, significant transfer was observed. However,
when the formation of fusion pores was examined with hydrophilic
fluorescent calcein, transfer from erythrocytes to HA-expressing cells
was not observed with the mutant carrying six histidine residues. The
addition of different amino acids to the cytoplasmic tail of HA caused
an inhibitory effect similar to that caused by the addition of His. On
the other hand, a mutant lacking the cytoplasmic tail was still able to fuse at a reduced level. These results demonstrate that elongation of
the cytoplasmic tail interferes with the formation and enlargement of
fusion pores. Thus, the length of the cytoplasmic tail plays a critical
role in the fusion process.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Elongation of the Cytoplasmic Tail Interferes with
the Fusion Activity of Influenza Virus Hemagglutinin


*
Corresponding author. Mailing address: Institut
für Virologie, Philipps-Universität Marburg, Postfach 2360, 35011 Marburg, Germany. Phone: (6421) 28 6253. Fax: (6421) 28 8962. E-mail: KLENK{at}mailer.uni-marburg.de.
Present address: Department of Microbiology, Kawasaki Medical
School, Matsushima 577, Kurashiki, Okayama 70101, Japan.
Present address: Tokyo Metropolitan Institute for Neuroscience,
2-6 Musashidai, Fuchu, Tokyo 183, Japan.
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