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Journal of Virology, August 1999, p. 6474-6483, Vol. 73, No. 8
Department of Molecular Genetics and
Microbiology, University of Florida College of Medicine,
Gainesville, Florida 32610
Received 8 February 1999/Accepted 3 May 1999
The Sendai virus P protein is an essential component of the viral
RNA polymerase (P-L complex) required for RNA synthesis. To identify
amino acids important for P-L binding, site-directed mutagenesis of the
P gene changed 17 charged amino acids, singly or in groups, and two
serines to alanine within the L binding domain from amino acids 408 to
479. Each of the 10 mutants was wild type for P-L and P-P protein
interactions and for binding of the P-L complex to the nucleocapsid
template, yet six showed a significant inhibition of in vitro mRNA and
leader RNA synthesis. To determine if binding was instead hydrophobic
in nature, five conserved hydrophobic amino acids in this region were
also mutated. Each of these P mutants also retained the ability to bind
to L, to itself, and to the template, but two gave a severe decrease in
mRNA and leader RNA synthesis. Since all of the mutants still bound L,
the data suggest that L binding occurs on a surface of P with a complex
tertiary structure. Wild-type biological activity could be restored for
defective polymerase complexes containing two P mutants by the addition
of wild-type P protein alone, while the activity of two others could
not be rescued. Gradient sedimentation analyses showed that rescue was
not due to exchange of the wild-type and mutant P proteins within the
P-L complex. Mutants which gave a defective RNA synthesis phenotype and
could not be rescued by P establish an as-yet-unknown role for P within
the polymerase complex, while the mutants which could be rescued define
regions required for a P protein function independent of polymerase function.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Dissection of Individual Functions of the Sendai
Virus Phosphoprotein in Transcription
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Microbiology, University of Florida College of Medicine, P.O. Box 100266, Gainesville, FL 32610. Phone: (352) 392-3131. Fax: (352) 846-2042. E-mail:
smoyer{at}medmicro.med.ufl.edu.
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