Disease relevance of Trl

• Binding of the GAGA transcription factor on existing nucleosomes leads to nucleosome disruption, DNase I hypersensitivity at the TATA box and heat-shock elements, and rearrangement of adjacent nucleosomes [1].

High impact information on Trl

• GAGA factor associates with euchromatic genes that are enriched in (GA)n motifs [2].
• One factor, which binds to multiple GAGA DNA sequence motifs in the Ubx promoter, has been purified and shown to activate transcription from this promoter in a binding site-dependent manner [3].
• The Trithorax-like gene we described here is required for the normal expression of the homeotic genes and is a modifier of position-effect variegation [4].
• Our genetic analysis suggests that the chromatin modelling function of the GAGA factor is not restricted to promoter regions [4].
• Drosophila GAGA factor directs chromatin remodeling to its binding sites [5].

Biological context of Trl

• Chromatin immunoprecipitation experiments indicated the presence of the GAGA factor-FACT complex in the regulatory regions of Ultrabithorax and Abdominal-B [5].
• Drosophila FACT contributes to Hox gene expression through physical and functional interactions with GAGA factor [5].
• Co-localization of Polycomb protein and GAGA factor on regulatory elements responsible for the maintenance of homeotic gene expression [6].
• We propose that GAGA factor binds constitutively to regulatory elements in the bithorax complex, which function both as PREs and as trithorax group response elements [6].
• The GAGA factor and Batman codistribute on polytene chromosomes, coimmunoprecipitate from nuclear embryonic and larval extracts, and interact in the yeast two-hybrid assay [7].

Anatomical context of Trl

• Thereafter, both GAGA proteins are present in nearly equal amounts throughout development; in larval salivary gland nuclei they colocalize completely to specific regions along the euchromatic arms of the polytene chromosomes [8].
• Mouse unfertilized eggs and one-cell and two-cell embryos display a GAGA box-binding activity of maternal origin that disappears at the four-cell stage and is also abundant in the gonads, but is barely detectable in other adult tissues [9].
• In vivo titrations of Adf-2 activity with the Adf-2 motif by transient co-transfection competitions in different Drosophila cell lines suggested that Adf-2 is a cell-specific repressor [10].

Associations of Trl with chemical compounds

• Intron binding occurs equally frequently in last introns compared with first introns, suggesting that GAF may not only regulate transcription initiation, but possibly also elongation [11].
• Functional mapping of the GAGA factor assigns its transcriptional activity to the C-terminal glutamine-rich domain [12].
• The affinity of GAGA for triplexes of the purine motif, such as a d[AG(GA.TC)]22 intermolecular triplex, is significantly lower [13].

Physical interactions of Trl

• We show that this domain is involved in the interaction between Batman and the DNA binding GAGA factor encoded by the Trithorax-like gene [7].
• The GAGA factor of Drosophila interacts with SAP18, a Sin3-associated polypeptide [14].
• Using two different transgene assays we demonstrate that GAGA-factor-binding sites are necessary but not sufficient for full Fab-7 enhancer-blocking activity [15].
• Other fragments lack GAGA binding sites but can still bind PcG complexes in vitro [16].
• The GAGA factor of Drosophila is a sequence-specific DNA-binding protein that contributes to multiple processes from the regulation of gene expression to the structural organisation of heterochromatin and chromatin remodelling [17].

Regulatory relationships of Trl

• These observations suggest a possible mechanism of how Trl-GAGA plays a role in maintaining the repressed state of target genes involving lolal, which may function as a mediator to recruit PcG complexes [18].
• tramtrack 69 (TTK69) is known to repress GAGA-mediated activation of the eve promoter in S2 cells [19].
• Moreover, a fusion protein in which the POZ/BTB domain of GAGA is replaced by that of TTK69 is not capable of activating the eve promoter but efficiently represses GAGA-dependent activation [19].

Other interactions of Trl

• In order to understand how Trl-GAGA functions in PcG context, we have looked for the interactors of this protein [18].
• Here, we show that mutant alleles of Trl, dsap18 and drpd3/hdac1 enhance A6-to-A5 transformation indicating a contribution to the regulation of Abd-B expression at A6 [20].
• Batman, together with the GAGA factor, binds to MHS-70, a 70-bp fragment of the bithoraxoid Polycomb response element [7].
• The first 245 residues of GAGA, including the POZ domain, are necessary and sufficient to bind dSAP18 [14].
• The Drosophila Corto protein interacts with Polycomb-group proteins and the GAGA factor [21].

Analytical, diagnostic and therapeutic context of Trl

• Electron microscopy revealed that GAGA binds to multiple sites as a large oligomer and induces bending of the promoter DNA [22].
• Protein cross-linking and gel filtration chromatography experiments established that the POZ domain is required for GAGA oligomerization into higher order complexes [22].
• We purified Adf-2 through multiple rounds of sequence-specific DNA affinity chromatography [10].
• Moreover, a simple synthetic GAG sequence is sufficient to bind GAF in vitro . Here we directly compare the affinity of GAF for different sequence elements by immunoprecipitation and gel mobility shift analysis [23].
• The DNA sequence C/AGAGCGC/AGA, related to binding sites for GAF and Zeste transcription factors, was selected from a pool of degenerate PCR fragments for binding to the cytoplasmic protein of Drosophila preblastoderm embryos [24].

References