Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06510.
J Virol 65: 4033-41 (1991)
Abstract
Epstein-Barr virus (EBV) encodes a protein, ZEBRA, which enables the
virus to switch from a latent to a lytic life cycle. The basic domain of
ZEBRA is homologous to the Fos/Jun oncogene family, and both proteins
bind the canonical AP-1 site (TGAGTCA). However, ZEBRA does not contain
a leucine zipper dimerization domain which has been shown to be
necessary for DNA binding of Fos/Jun proteins. Additionally, ZEBRA binds
to sites which deviate from the AP-1 consensus sequence. Thus, it was
of interest to define the domain of the ZEBRA protein required for DNA
binding. We have determined by mutagenesis that ZEBRA residues 172 to
227, representing the basic domain and a putative dimerization domain,
are required for specific binding to AP-1 and divergent sites.
Mutagenesis of the basic amino acids 178 to 180 or 187 to 189 abrogates
ZEBRA binding to all DNA target sequences. These residues are conserved
in Fos and are also necessary for Fos DNA-binding activity. We have
found that a Fos-GCN4 chimera and ZEBRA have different cognate binding
specificities. The autoregulated BZLF1 promoter contains three divergent
AP-1 sequences, ZIIIA (TGAGCCA), ZIIIB (TTAGCAA), and Z-AP-1-octamer
(TGACATCA). ZEBRA binds with high specificity to ZIIIA and ZIIIB but
weakly to the Z-AP-1 octamer. Conversely, the Fos-GCN4 chimera
recognizes only the Z-AP-1 octamer. ZEBRA binds the ZIIIA and ZIIIB
sites together in a noncooperative fashion, while Fos-GCN4 binds these
sites as a higher-order complex. Additionally, we have found that
flanking sequences influence binding of Fos-GCN4 to a degenerate AP-1
site (TGAGCAA). The characteristic binding specificities of ZEBRA and
cellular AP-1 proteins suggest that they differentially affect viral and
cellular transcription.
Mesh Headings
Unique Identifier: 91303651
Chemical Identifiers (Names)