J Virol, May 1998, p. 3837-3844, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Dipartimento di Medicina Sperimentale e Diagnostica, Sezione di Microbiologia, Università di Ferrara, Ferrara, Italy
Received 22 December 1997/Accepted 30 January 1998
To define the molecular features characteristic of the early stages
of infection of lymphocytes with human herpesvirus 6 (HHV-6) variant A
or B, we studied the temporal regulation of expression of selected sets
of viral genes. Thus, U42, U94, U89-U90, U73, and U39 are
genes
since their transcripts (i) were made in the presence of inhibitors of
protein synthesis and (ii) were detected 3 h after infection of
untreated cells. U41, U53, U31, and U19 are
genes since their
expression is inhibited by cycloheximide but not by phosphonoacetate,
an inhibitor of DNA synthesis. U100 is a
gene since its spliced
transcript encoding the structural glycoprotein gp82/105 was first
detected 16 h after infection of untreated cells but could not be
detected in cells treated with phosphonoacetate. HHV-6 variants differ
in the transcription patterns of their genes. U16-U17 originates a
splice transcript and is regulated as
in HHV-6B and as
in
HHV-6A. U91 generates two transcripts, amplified as 476- and 374-bp PCR
fragments. The 476-bp fragment is
in HHV-6A-infected cells but
in HHV-6B-infected cells. Conversely, the 374-bp fragment is
in
HHV-6A-infected cells and
in HHV-6B-infected cells. Furthermore,
the spliced product of U18-U19-U20 (526 bp) is
in HHV-6A-infected
cells, but only a partially spliced form (1.9 kb) was detected at late stages of infection in HHV-6B. HHV-6 transcription was also studied in
nonproductive lymphoid cells, and the same transcription pattern detected during lytic infection was observed. Also, HHV-6 variants maintain the differences in U91, U16-17, and U18-U19-U20. We conclude that, as expected from the sequencing data, gene expression is generally similar in HHV-6 variants. However, transcription of selected
genes in HHV-6A and HHV-6B differs with respect to temporal regulation
and splicing pattern. Furthermore, the identification of viral
functions expressed during the different stages of lytic replication
suggests that reverse transcription-PCR for HHV-6 genes is a useful
diagnostic approach to differentiate between latent and productive
HHV-6 infection.
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