Skip to main content
. 2013 Jun 3;288(28):20633–20645. doi: 10.1074/jbc.M113.452813

FIGURE 7.

FIGURE 7.

A model for the regulation of transcriptional induction of ICL1 and FBP1 by the PIPTC. A schematic model for the PIPTC-mediated regulation of chromatin architecture at the ICL1/FBP1 promoter is presented. ICL1 and FBP1 contain a positive (CSRE) and a negative (URE) transcriptional regulatory element at their promoters. The CSRE binds to Cat8 or Sip4 transcriptional activators. The URE binds to the Mig1/2 transcriptional repressor. FBP1 and ICL1 belong to TATA box-containing genes that have the +1 nucleosome positioned at the TSS and depend on SAGA rather than transcription factor IID to establish the PIC. In glucose-rich medium, glycolysis is actively functional (ON) (left). Gluconeogenesis is inactive (OFF), and transcription of ICL1 and FBP1 is repressed by the Mig1/2-Cyc8-Tup1 complex. Transcription of CAT8 and SIP4 is repressed in glucose-rich medium, and therefore transcriptional activation function from the CSRE at the ICL1/FBP1 promoter is tenuous. In non-glucose carbon medium, in which glycolysis is no longer functional (OFF), gluconeogenesis is activated (ON) (right). The Cyc8-Tup1 corepressor is converted to the Cti6-Cyc8-Tup1 coactivator by the PIPTC at the late endosomal/vacuolar membrane. The PIPTC appears to play a critical role in remodulating the chromatin architecture at the ICL1 and FBP1 promoters to a promoter structure more accessible to the Cat8 and Sip4 activators. The Cti6-Cyc8-Tup1 coactivator and the Cat8/Sip4 activators recruit the SAGA coactivator complex to the ICL1 and FBP1 promoters, presumably through the interaction between Tra1 of the SAGA complex and Cti6 or Cat8/Sip4 proteins. Inferring from the characterized features at the GAL1 promoter, we predict that SAGA may recruit the Swi/Snf nucleosome remodeler that evicts the +1 nucleosome positioning at the TSS and opens the promoter to establish the PIC. Both the PIPTC and the Cat8/Sip4-dependent activation pathway play critical roles in robustly establishing the activated state (right) from the repressed state (left) of chromatin architecture at the ICL1 and FBP1 promoters. PI(3)P, phosphatidylinositol 3-phosphate.