A tryptophan-rich peptide acts as a transcription activation domain

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 W5) significantly enhanced its activity (~1.8-fold), while mutations which substituted aromatic residues with alanine residues severely impaired its activity. Accordingly, a much more active peptide, pentatryptophan (W7), was produced, which elicited ~3-fold higher activity than that of the native pentapeptide and the N domain. Further study indicated that W7 mediates transcription activation through interacting with the general transcription factor, TFIIB.Since W7 shares no sequence homology or features with any known transcription activators, it may represent a novel class of AD.Eukaryotic transcriptional activators that stimulate transcription initiation of a particular set of target genes usually consist of a sequence-specific DNA-binding domain (DBD) and a transcription activation domain (AD). The DBD targets these activators to a specific location in the promoter region of a gene, and the AD mediates transcription initiation by recruiting gene-specific factors, chromatin-remodeling factors, mediator complexes, and general transcription factors [1,2]. DBDs are classified into several distinct patterns or motifs according to their sequences and structural similarities. In contrast, ADs do not share significant sequence homologies, and therefore no specific motif has been defined. Despite this, several classes of ADs with distinctive sequence features were identified, including acidic activators [3], glutamine-rich activators [4], and pro