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J. Virol., 12 1996, 8564-8570, Vol 70, No. 12
OC Richards, S Baker and E Ehrenfeld
The poliovirus 3D RNA-dependent RNA polymerase contains two peptide
segments previously shown to cross-link to nucleotide substrates via lysine
residues. To determine which lysine residue(s) might be implicated in
catalytic function, we engineered mutations to generate proteins with
leucine residues substituted individually for each of the lysine residues
in the NTP binding regions. These proteins were expressed in Escherichia
coli and were examined for their abilities to bind nucleotides and to
catalyze RNA chain elongation in vitro. Replacement of each lysine residue
in the NTP binding segment located in the central portion of the 3D
molecule (Lys-276, -278, or -283) with leucine produced no impairment of
GTP binding or polymerase activity. Substitution of leucine for Lys-61 in
the N-terminal portion of the protein, however, abolished the binding of
protein to GTP-agarose and all detectable polymerase activity. A nearby
lysine replacement with leucine at position 66 had no effect on enzyme
activity. The three mutations in the central region of 3D were introduced
into full-length viral cDNAs, and the infectivities of RNA transcripts were
examined in transfected HeLa cells. Growth of virus containing 3D with a
mutation at residue 278 (3Dmu278) or 3Dmu283 was indistinguishable from
that of the wild type; however, 3Dmu276 generated extremely slow-growing,
small- plaque virus. Polyprotein processing by 3CDmu276 was unaffected.
Large- plaque variants, in which the Leu-276 codon had mutated again to an
arginine codon, emerged at high frequency. The results suggest that a
lysine residue at position 61 of 3Dpol is essential for polymerase
catalytic function and that a basic (lysine or arginine) residue at
position 276 is required for some other function of 3D important for virus
growth but not for RNA chain elongation or polyprotein processing.
Copyright © 1996, American Society for Microbiology
Mutation of lysine residues in the nucleotide binding segments of the poliovirus RNA-dependent RNA polymerase
Department of Molecular Biology and Biochemistry, University of California, Irvine 92697, USA.
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