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J. Virol., 12 1996, 8340-8347, Vol 70, No. 12
RT Sarisky, Z Gao, PM Lieberman, ED Fixman, GS Hayward and SD Hayward
The Zta transactivator is crucial for both Epstein-Barr virus (EBV) lytic
gene expression and lytic DNA replication. We have used a
cotransfection-replication assay to examine the effect of mutations in the
Zta activation domain (amino acids [aa] 1 to 167) on Zta replication
activity. Deletion of Zta aa 25 to 86, which are critical for
transcriptional activation of ori-Lyt, or aa 93 to 141 did not adversely
affect replication of an ori-Lyt-containing target plasmid. However,
removal of aa 2 to 25 (delta2-25) abolished replication activity. Within
this subdomain, deletion of aa 2 to 10 (delta2-10) or mutation of codons 18
and 19 (m18/19) or 22 and 26 (m22/26) did not affect replication
competency, while deletion of codons 13 to 19 (delta13-19) or mutation at
codons 12 and 13 (m12/13) impaired Zta replication function. Each of the
replication-negative Zta variants was capable of transactivating expression
from both BHLF1 promoter- chloramphenicol acetyltransferase constructions
and the BMRF1 promoter on endogenous EBV genomes in Raji cells with
efficiency comparable to that of the wild-type polypeptide. Thus, a
replication contribution of Zta was functionally separable from its
transactivation activity and was supplied by the N-terminal region
encompassing aa 11 to 25. Replication by a subset of the impaired Zta
mutants was partially rescued upon the addition of Rta to the replication
assay. The contribution of Rta mapped to domain II of the Rta activation
domain and was specific for this region. A chimeric Rta-EBNA-2
transactivation domain fusion, which retains the DNA-binding and
transactivation properties associated with wild-type Rta, failed to rescue
replication- deficient Zta. Our data suggest that Rta may act as an
ancillary replication factor in EBV ori-Lyt DNA synthesis by stabilizing
Zta- replisome interactions.
Copyright © 1996, American Society for Microbiology
A replication function associated with the activation domain of the Epstein-Barr virus Zta transactivator
Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205-2185, USA.
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