Tetrahymena General Control Non-Derepressor 5 (tGCN5) is a critical regulator of gene transcription via acetylation of histones Since the acetylation ability has been attributed to the "core region", we perform mutagenesis of residues within the tGCN5 "core region" in order to identify those critical for function and stability Residues that do not participate in catalysis are identified, mutated and characterized for activity, structure and thermodynamic stability Variants 1107V, Q114L, A121T and A130S maintain the acetylation function relative to wild-type tGCN5, while variants F90Y, F112R and R140H completely abolish function Of the three non-functional variants, since F112 is mutated into a non-homologous charged residue, a loss in function is expected. However, the remaining two variants are mutated into homologous residues, suggesting that F90 and R140 are critical for the activity of tGCN5 While mutation to homologous residue maintains acetylation of histone H3 for the majority of the variants, the two surface-exposed residues. F90 and R140, appear to be essential for tGCN5 function, structure or stability. (C) 2010 Elsevier Inc All rights reserved