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Journal of Virology, July 2000, p. 6006-6014, Vol. 74, No. 13
Laboratory of Infectious Diseases, National Institute of
Allergy and Infectious Diseases, Bethesda, Maryland
20892-07201 and Department of Immunology
and Microbiology, Rush-Presbyterian-St. Luke's Medical Center,
Chicago, Illinois 606122
Received 9 February 2000/Accepted 12 April 2000
The promoters involved in transcription and RNA replication by
respiratory syncytial virus (RSV) were examined by using a plasmid-based minireplicon system. The 3' ends of the genome and antigenome, which, respectively, contain the 44-nucleotide (nt) leader (Le) and 155-nt trailer-complement (TrC) regions, should each
contain a promoter for RNA replication. The 3' genome end also should
have the promoter for transcription. Substitution for the Le with
various lengths of TrC demonstrated that the 3'-terminal 36 nt of TrC
are sufficient for extensive (but not maximal) replication and that
when juxtaposed with a transcription gene-start (GS) signal, this
sequence was also able to direct transcription. It was also shown that
the region of Le immediately preceding the GS signal of the first gene
could be deleted with either no effect or with a slight decrease in
transcription initiation. Thus, the TrC is competent to direct
transcription even though it does not do so in nature, and the partial
sequence identity it shares with the 3' end of the genome likely
represents the important elements of a conserved promoter active in
both replication and transcription. Increasing the length of the
introduced TrC sequence incrementally to 147 nt resulted in a fourfold
increase in replication and a nearly complete inhibition of
transcription. These two effects were unrelated, implying that
transcription and replication are not interconvertible processes
mediated by a common polymerase, but rather are independent processes.
The increase in replication was specific to the TrC sequence, implying
the presence of a nonessential, replication-enhancing
cis-acting element. In contrast, the inhibitory effect on
transcription was due solely to the altered spacing between the 3' end
of the genome and GS signal, which implies that the transcriptase
recognizes the first GS signal as a promoter element. Neither the
enhancement of replication nor the inhibition of transcription was due
to increased base-pairing potential between the 3' and 5' ends. The
relative strengths of the Le and TrC promoters for directing RNA
synthesis were compared and found to be very similar. Thus, these
findings highlighted a high degree of functional similarity between the
RSV antigenomic and genomic promoters, but
provided a further distinction between promoter requirements for
transcription and replication.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Functional Analysis of the Genomic and Antigenomic
Promoters of Human Respiratory Syncytial Virus
*
Corresponding author. Mailing address: 7 Center Dr. MSC
0720, Bethesda, MD 20892-0720. Phone: (301) 496-3481. Fax: (301)
496-8312. E-mail: pcollins{at}niaid.nih.gov.
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