The Epstein-Barr virus Zta transactivator: a member of the bZIP family with unique DNA-binding specificity and a dimerization domain that lacks the characteristic heptad leucine zipper motif.
Introduction of the zta gene of Epstein-Barr virus into latently infected B cells leads to induction of the entire lytic cycle program of the virus. The Zta gene product is a sequence-specific DNA-binding protein of 35 kilodaltons that behaves as a specific transcriptional transactivator in transient cotransfection assays. All known Zta-responsive target promoters contain one or more members of a family of consensus-binding sites known as ZREs. On the basis of the presence of limited amino acid similarity within a basic carboxy-terminal domain, Zta has been proposed to be a highly divergent member of the c-Jun/c-Fos/GCN4 family of AP-1-binding proteins. We show here that in vitro-translated Zta and the Jun:Fos proteins have overlapping but distinct target DNA-binding specificies; both recognize canonical AP-1 sites, but only Zta recognizes ZRE sites and only Jun:Fos recognizes CRE sites. The relative binding affinity of Zta for oligonucleotides containing the 7-base-pair c-Fos AP-1 site TGAGTCA was twofold greater than that for the ZRE core motifs TGAGCAA, TG TGCAA, and TGAGTAA, but 10-fold greater than that for TGTGTCA, as measured by gel mobility retardation and competition DNA-binding assays. Cross-linking and cotranslational heterodimerization assays showed that like GCN4, Zta forms a stable homodimer in both its DNA-bound and unbound forms. Furthermore, we show that a potential coiled-coil helical domain adjacent to the basic domain of Zta can substitute for the leucine zipper of c-Fos to produce a DNA-binding protein that has a very stringent target DNA specificity and can only recognize symmetric 9-base-pair AP-1 sites (ATGAGTCAT). Therefore, despite the absence of the repeated heptad leucine zipper motifs, the Zta protein retains the characteristic features of a juxtaposed basic region and an exactly aligned coiled-coil alpha-helical dimerization domain of the bZIP class of transcriptional regulatory factors.
Chang
Y N
YN
Department of Pharmacology, and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Dong
D L
DL
Hayward
G S
GS
Hayward
S D
SD
D000595:Amino Acid Sequence; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004854:Herpesvirus 4, Human / Q000235:genetics*; D007930:Leucine; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D005810:Multigene Family; D015345:Oligonucleotide Probes; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D012045:Regulatory Sequences, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D015345:Oligonucleotide Probes; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D004247:DNA; D007930:Leucine