AP2XII4

AP2XII-4 is a nuclear ApiAP2 transcription factor in Toxoplasma gondii that is one of ~24 AP2 transcription factors forming a series through the tachyzoite cell cycle, with successive sharp peaks of protein expression correlated with mRNA timing, consistent with a role mediated by AP2 domains with different promoter recognition specificities during coordinated cell cycle progression (PMID:20865045). It associates with the lysine acetyltransferase GCN5b in a distinct multi-subunit transcriptional complex; reciprocal co-immunoprecipitation of AP2XII-4 delineated its interactome, and together with the AP2IX-7-containing complex, suggests GCN5b is present in at least two distinct complexes characterized by different pairs of AP2 factors, implicating AP2XII-4 in GCN5b-mediated epigenetic gene regulation (PMID:31381949). The precise DNA targets and the functional consequences of its GCN5b association have not been directly characterized in the available corpus.

1. 2010 Low

   Before functional data existed, it was unknown whether AP2XII-4 participated in ordered cell-cycle gene control; expression profiling placed it within a series of AP2 factors peaking at successive cell-cycle points, framing it as a candidate stage-specific regulator.

   Evidence Genome-wide cell cycle transcriptome and protein expression timing analysis in dividing tachyzoites

   PMID:20865045

   Open questions at the time

   • Correlative timing only, no direct perturbation of AP2XII-4
   • No DNA target or binding motif established
   • Does not distinguish causal role from co-regulation
2. 2019 Medium

   It was unknown how AP2XII-4 exerts transcriptional effects at chromatin; reciprocal Co-IP/MS placed it in a distinct GCN5b-containing complex, linking it to acetyltransferase-mediated epigenetic regulation.

   Evidence Reciprocal co-immunoprecipitation with mass spectrometry under tachyzoite and bradyzoite-inducing conditions

   PMID:31381949

   Open questions at the time

   • Functional consequence of GCN5b association for target gene acetylation not demonstrated
   • Full subunit composition and stoichiometry of the complex not resolved
   • Whether AP2XII-4 recruits GCN5b to specific promoters untested