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Mol. Cell. Biol., 04 1995, 1923-1932, Vol 15, No. 4
NB Haas, CA Cantwell, PF Johnson and JB Burch
The PAR subfamily of basic leucine zipper (bZIP) factors comprises three
proteins (VBP/TEF, DBP, and HLF) that have conserved basic regions flanked
by proline- and acidic-amino-acid-rich (PAR) domains and functionally
compatible leucine zipper dimerization domains. We show that VBP
preferentially binds to sequences that consist of abutted GTAAY half-sites
(which we refer to as PAR sites) as well as to sequences that contain
either a C/EBP half-site (GCAAT) or a CREB/ATF half-site (GTCAT) in place
of one of the PAR half-sites. Since the sequences that we describe as PAR
sites and PAR-CREB/ATF chimeric sites, respectively, were both previously
described as high-affinity binding sites for the E4BP4 transcriptional
repressor, we infer that these sequences may be targets for positive and
negative regulation. Similarly, since the sequences that we describe as
PAR-C/EBP and PAR- CREB/ATF chimeric sites are known to be high-affinity
binding sites for C/EBP and CREB/ATF factors, respectively, we infer that
these sites may each be targets for multiple subfamilies of bZIP factors.
To gain insights regarding the molecular basis for the binding-site
specificity of PAR factors, we also carried out an extensive mutational
analysis of VBP. By substituting five amino acid residues that differ
between the Drosophila giant bZIP factor and the vertebrate PAR bZIP
factors, we show that the fork region, which bridges the basic and leucine
zipper domains, contributes to half-site sequence specificity. In addition,
we report that at least two domains amino terminal to the core basic region
are required for VBP to bind to the full spectrum of PAR target sites.
Thus, whereas direct base contacts may be restricted to basic- region
residues (as indicated by GCN4-DNA crystal structures), several other
domains also influence the DNA-binding specificity of PAR bZIP proteins.
Copyright © 1995, American Society for Microbiology
DNA-binding specificity of the PAR basic leucine zipper protein VBP partially overlaps those of the C/EBP and CREB/ATF families and is influenced by domains that flank the core basic region
Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
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