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. 2009 Jun 2;284(30):19856–19866. doi: 10.1074/jbc.M109.025817

FIGURE 8.

FIGURE 8.

Hypothetical model of transcriptional regulation of cell cycle arrest gene p21 by ZBTB5. A, p53 pathway and ZBTB5 targets. ZBTB5 represses transcription of the HDM2 and p21 genes. Solid line with arrowhead (→), transcriptional activation; solid line with ⊥, transcriptional repression. Solid line with double arrowhead (↔), molecular interaction. B, hypothetical model of transcriptional repression of p21 by ZBTB5 under three different cellular conditions. ZBTB5 represses transcription of cell cycle arrest gene p21 by binding to the two distal p53 binding elements by competition with p53. ZBTB5 also binds to the proximal Sp1 binding GC-box 5/6, with an unclear function in the transcriptional repression of the endogenous p21 gene by ZBTB5. ZBTB5 recruits co-repressor-HDAC complexes, which deacetylate histones Ac-H3 and Ac-H4 at the proximal promoter to repress transcription. Tsp +1, transcription start site. ZF, zinc finger DNA binding domain. ×, transcription repression.