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Journal of Virology, January 2000, p. 997-1003, Vol. 74, No. 2
Department of Plant Pathology, University of
Kentucky, Lexington, Kentucky 40546
Received 7 July 1999/Accepted 4 October 1999
The undivided double-stranded RNA (dsRNA) genome of
Helminthosporium victoriae 190S virus (Hv190SV) (genus
Totivirus) consists of two large overlapping open reading
frames (ORFs). The 5'-proximal ORF encodes a capsid protein (CP), and
the downstream, 3'-proximal ORF encodes an RNA-dependent RNA polymerase
(RDRP). Unlike the RDRPs of some other totiviruses, which are expressed
as a CP-RDRP (Gag-Pol-like) fusion protein, the Hv190SV RDRP is
detected only as a separate, nonfused polypeptide. In this study, we
examined the expression of the RDRP ORF fused in frame to the coding
sequence of the green fluorescent protein (GFP) in bacteria and
Schizosaccharomyces pombe cells. The GFP fusions were
readily detected in bacteria transformed with the monocistronic
construct RDRP:GFP; expression of the downstream RDRP:GFP from the
dicistronic construct CP-RDRP:GFP could not be detected. However,
fluorescence microscopy and Western blot analysis indicated that
RDRP:GFP was expressed at low levels from its downstream ORF in the
dicistronic construct in S. pombe cells. No evidence that
the RDRP ORF was expressed from a transcript shorter than the
full-length dicistronic mRNA was found. A coupled termination-reinitiation mechanism that requires host or eukaryotic cell factors is proposed for the expression of Hv190SV RDRP.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Expression of the Totivirus Helminthosporium
victoriae 190S Virus RNA-Dependent RNA Polymerase from Its
Downstream Open Reading Frame in Dicistronic Constructs
*
Corresponding author. Mailing address: Department of
Plant Pathology, University of Kentucky, S-305 Agriculture Science
Building-North, Lexington, KY 40546-0091. Phone: (606) 257-5969. Fax:
(606) 323-1961. E-mail: saghab00{at}pop.uky.edu.
Publication no. 99-12-92 of the Kentucky Agricultural Experiment Station.
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