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J. Virol., Nov 1997, 8167-8175, Vol 71, No. 11
AK Pattnaik, L Hwang, T Li, N Englund, M Mathur, T Das and AK Banerjee
Phosphorylation by casein kinase II at three specific residues (S-60, T-
62, and S-64) within the acidic domain I of the P protein of Indiana
serotype vesicular stomatitis virus has been shown to be critical for in
vitro transcription activity of the viral RNA polymerase (P-L) complex. To
examine the role of phosphorylation of P protein in transcription as well
as replication in vivo, we used a panel of mutant P proteins in which the
phosphate acceptor sites in domain I were substituted with alanines or
other amino acids. Analyses of the alanine- substituted mutant P proteins
for the ability to support defective interfering RNA replication in vivo
suggest that phosphorylation of these residues does not play a significant
role in the replicative function of the P protein since these mutant P
proteins supported replication at levels > or = 70% of the wild-type
P-protein level. However, the transcription function of most of the mutant
proteins in vivo was severely impaired (2 to 10% of the wild-type P-protein
level). The level of transcription supported by the mutant P protein
(P(60/62/64)) in which all phosphate acceptor sites have been mutated to
alanines was at best 2 to 3% of that of the wild-type P protein. Increasing
the amount of P(60/62/64) expression in transfected cells did not rescue
significant levels of transcription. Substitution with other amino acids at
these sites had various effects on replication and transcription. While
substitution with threonine residues (P(TTT)) had no apparent effect on
transcription (113% of the wild-type level) or replication (81% of the
wild-type level), substitution with phenylalanine (P(FFF)) rendered the
protein much less active in transcription (< 5%). Substitution with
arginine residues led to significantly reduced activity in replication
(6%), whereas glutamic acid substituted P protein (P(EEE)) supported
replication (42%) and transcription (86%) well. In addition, the mutant P
proteins that were defective in replication (P(RRR)) or transcription
(P(60/62/64)) did not behave as transdominant repressors of replication or
transcription when coexpressed with wild-type P protein. From these
results, we conclude that phosphorylation of domain I residues plays a
major role in in vivo transcription activity of the P protein, whereas in
vivo replicative function of the protein does not require phosphorylation.
These findings support the contention that different phosphorylated states
of the P protein regulate the transcriptase and replicase functions of the
polymerase protein, L.
Copyright © 1997, American Society for Microbiology
Phosphorylation within the amino-terminal acidic domain I of the phosphoprotein of vesicular stomatitis virus is required for transcription but not for replication
Department of Microbiology and Immunology, University of Miami School of Medicine, Florida 33101, USA. apattnai@mednet.med.miami.edu
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