p29ING4 and p28ING5 bind to p53 and p300, and enhance p53 activity.

We identified and characterized two new ING family genes, p29ING4 and p28ING5,coding for two proteins of 249 and 240 amino acids, respectively. Both p29ING4 and p28ING5 proteins have a plant homeodomain finger motif also found in other ING proteins, and which is common in proteins involved in chromatin remodeling. p29ING4 or p28ING5 overexpression resulted in a diminished colony-forming efficiency, a decreased cell population in S phase, and the induction of apoptosis in a p53-dependent manner. Both p29ING4 and p28ING5 activate the p21/waf1 promoter, and induce p21/WAF1 expression. p29ING4 and p28ING5 enhance p53 acetylation at Lys-382 residues, and physically interact with p300, a member of histone acetyl transferase complexes, and p53 in vivo. These results indicate that p29ING4 and p28ING5 may be significant modulators of p53 function.