Molecular and genetic characterization of GABP beta.

Abstract

This report outlines three observations relating to GABPI3 , a polypeptide constituent of the heterotetrameric transcription factor GABP. Evidence is presented showing that the mouse genome encodes two highly related GABPI3 polypeptides, designated GABPI31-1 and GABPI32-1. Genomic and eDNA copies of the newly defined Gabpb2 gene were cloned and characterized, providing the conceptually translated amino acid sequence of GABPI32-1. The genes encoding these two proteins, as well as GABPc~, were mapped to three unlinked chromosomal loci. Although physically unlinked, the patterns of expression of the three genes were strikingly concordant. Finally, the molecular basis of GABPI3 dimerization was resolved. Carboxy-terminal regions of the two GABPI3 polypeptides, which mediate dimerization, bear highly related primary amino acid sequences. Both sequences are free of oL-helix destabilizing residues and, when displayed on idealized c~-helical projections, reveal marked amphipathy. Two observations indicate that these regions adopt an a-helical conformation and intertwine as coiled-coils. First, the dimer-forming region of GABPI32-1 can functionally replace the leucine zipper of a bZIP transcription factor. Second, a synthetic peptide corresponding to this region shows distinctive helical properties when examined by circular dichroism spectroscopy. Finally, evidence is presented showing that GABPI31-1 and GABPI32-1 can heterodimerize through this carboxy-terminal domain, but neither protein can heterodimerize via the dimer-forming region of the bZIP protein C/EBPI3.

GA-binding protein α/β is a critical regulator of the BRCA1 promoter

“…GABPa/b is thought to bind as a heterotetramer consisting of two molecules of the DNA binding a subunit, and two molecules of either the b1 or b2 subunits, which are encoded by separate genes (de la Brousse et al, 1994). The tetramer is thought to bind preferentially to a tandem repeat of the recognition element, but several examples of GABPa/b binding to single elements have also been reported (Boccia et al, 1996;Nuchprayoon et al, 1997).…”

“…This ets site is most closely related to the recognition element for GABPa/ b, with the complementary strand sequence CGGAA-GAG, being identical to a GABPa/b element identi®ed in the COX4 gene (Virbasius et al, 1993). GABPa/b consists of a tetramer made up of two a DNA binding subunits, and two b subunits, with the b1-1 and b1-2 forms derived from di erential splicing of one gene and the b2-1 form derived from a separate gene (de la Brousse et al, 1994). The human forms of these proteins are known as hGABPa, while hGABPb1 is equivalent to the mouse GABP b1-1, and hGABPg1 is Figure 3 Activity of RIBS multimer constructs in MCF-7 and T-47D cell lines.…”

Synergistic Action of GA-Binding Protein and Glucocorticoid Receptor in Transcription from the Mouse Mammary Tumor Virus Promoter

“…Whether the mechanisms of transactivation would be the same when a steroid receptor plus GABP interacts with a TATA-box-containing promoter will have to be determined. GABP was found to be widely expressed in tissues (19,37), yet it has been shown to command the regulation of several genes which are expressed in celltype-specific patterns. Such selectivity depends in part on the nature of the DNA-GABP␣ interactions and on regulation imparted by its association with GABP␤ (28).…”

“…GABP forms an ␣2␤2 tetramer on tandemly arranged sites (like those in the immediate-early promoter of herpes simplex virus) through a leucine zipper domain at the carboxyl terminus of GABP␤ (19). As fp1 and fp2 form an analogous arrangement in the MMTV LTR, separated by 8 bp, we investigated the binding properties of a double-stranded oligonucleotide comprising both fp1 and fp2.…”

“…The ␤ subunit (GABP␤) is bound to GABP␣ via repeats of the Notch-ankyrin type (19). On two neighboring sites in the DNA, tetramers are formed by interaction between the ␤ subunits, and all these protein-protein interactions greatly stabilize the binding to DNA (reviewed in reference 28).…”