Background: Eukaryotic transcription activators normally consist of a sequence-specific DNA-binding domain (DBD) and a transcription activation domain (AD). While many sequence patterns and motifs have been defined for DBDs, ADs do not share easily recognizable motifs or structures. Results: We report herein that the N-terminal domain of yeast valyl-tRNA synthetase can function as an AD when fused to a DNA-binding protein, LexA, and turn on reporter genes with distinct LexA-responsive promoters. The transcriptional activity was mainly attributed to a five-residue peptide, WYDWW, near the C-terminus of the N domain. Remarkably, the pentapeptide per se retained much of the transcriptional activity. Mutations which substituted tryptophan residues for both of the non-tryptophan residues in the pentapeptide (resulting in W(5)) significantly enhanced its activity (similar to 1.8-fold), while mutations which substituted aromatic residues with alanine residues severely impaired its activity. Accordingly, a much more active peptide, pentatryptophan (W(7)), was produced, which elicited similar to 3-fold higher activity than that of the native pentapeptide and the N domain. Further study indicated that W(7) mediates transcription activation through interacting with the general transcription factor, TFIIB. Conclusions: Since W(7) shares no sequence homology or features with any known transcription activators, it may represent a novel class of AD.