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Journal of Virology, September 1998, p. 7270-7279, Vol. 72, No. 9
Sir Albert Sakzewski Virus Research Centre,
Royal Children's Hospital, Brisbane, Queensland 4029, Australia
Received 17 March 1998/Accepted 3 June 1998
A BHK cell line persistently expressing a Kunjin (KUN) virus
replicon RNA (repBHK, similar to our recently described ME/76Neo BHK cell line [A. A. Khromykh and E. G. Westaway, J. Virol. 71:1497-1505, 1997]) was used for rescue and propagation of
KUN viruses defective in the RNA polymerase gene (NS5). A new
infectious full-length KUN virus cDNA clone, FLSDX, prepared from
our previously described cDNA clone pAKUN (A. A. Khromykh and
E. G. Westaway, J. Virol. 68:4580-4588, 1994) and possessing
~105-fold higher specific infectivity than that of pAKUN,
was used for preparation of defective mutants. Deletions of the
predicted RNA polymerase motif GDD (producing FLdGDD) and
of one of the predicted methyltransferase motifs
(S-adenosylmethionine [SAM] binding site, producing
FLdSAM) were introduced separately into FLSDX. Transcription and
transfection of FLdGDD and FLdSAM RNAs into repBHK cells
but not into normal BHK cells resulted in their replication and the
recovery of defective viruses able to replicate only in repBHK cells.
Reverse transcription-PCR and sequencing analyses showed retention of
the introduced deletions in the genomes of the recovered viruses.
Retention of these deletions, as well as our inability to recover
viruses able to replicate in normal BHK cells after prolonged
incubation (for 7 days) of FLdGDD- or FLdSAM-transfected repBHK cells, excluded the possibility that recombination had occurred between the deleted defective NS5 genes present in transfected RNAs and the functional NS5 gene present in the
repBHK cells. An RNA with a point mutation in the GDD motif (FLGVD) was also complemented in transfected repBHK cells,
and defective virus was recovered by day 3 after transfection.
However, in contrast to the results with FLdGDD and FLdSAM
RNAs, prolonged (4 days or more) incubation of FLGVD RNA in
normal BHK cells allowed recovery of a virus in which the
GVD mutation had reverted via a single base change to the
wild-type GDD sequence. Overall, these results represent
the first demonstration of trans-complementation of
defective flavivirus RNAs with deleterious deletions in the flavivirus
RNA polymerase gene NS5. The complementation system described here may
prove to be useful for the in vivo complementation of deletions and
mutations affecting functional domains or the essential secondary
structure in any of the other flavivirus nonstructural proteins.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
trans-Complementation of Flavivirus RNA Polymerase
Gene NS5 by Using Kunjin Virus Replicon-Expressing BHK Cells
*
Corresponding author. Mailing address: Sir Albert
Sakzewski Virus Research Centre, Royal Children's Hospital, Herston
Rd., Brisbane, QLD 4029, Australia. Phone: (617) 3253-1568. Fax: (617) 3253-1401. E-mail: a.khromykh{at}mailbox.uq.edu.au.
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