P. Doring et al., The role of AHA motifs in the activator function of tomato heat stress transcription factors HsfA1 and HsfA2, PL CELL, 12(2), 2000, pp. 265-278
Using reporter assays in tobacco protoplasts and yeast, we investigated the
function of the acidic C-terminal activation domains of tomato heat stress
transcription factors HsfA1 and HsfA2. Both transcription factors contain
short, essential peptide motifs with a characteristic pattern of aromatic a
nd large hydrophobic amino acid residues embedded in an acidic context (AHA
motifs), The prototype is the AHA1 motif of HsfA2, which has the sequence
DDIWEELL. Our mutational analysis supports the important role of the aromat
ic and large hydrophobic amino acid residues in the core positions of the A
HA motifs, The pattern suggests the formation of an amphipathic, negatively
charged helix as the putative contact region with components of the basal
transcription complex, In support of this concept, proline or positively ch
arged residues in or adjacent to the AHA motifs markedly reduce or abolish
their activity. Both AHA motifs of HsfA1 and HsfA2 contribute to activator
potential, and they can substitute for each other; however, there is eviden
ce for sequence and positional specificity.