Generating yeast transcriptional activators containing no yeast protein sequences.

We previously reported that roughly 1% of the short peptides encoded by Escherichia coli genomic DNA fragments act as transcriptional activating regions in yeast when fused to GAL4(1-147), a DNA-binding portion of the yeast transcriptional activator GAL4 (ref. 1). Struhl questioned the conclusion that we had identified new transcriptional activating sequences that function in the absence of yeast transcriptional activating sequences. His criticism was based on two considerations: first, GAL4(1-147) contains an acidic segment (and subsequent experiments have shown that this region contains a weak activating region in vitro); second, attempts to isolate new activating regions failed when the DNA-binding domain of a bacterial repressor, LexA(1-87), was used as the DNA-binding unit. We report here a repeat of our original experiment using the complete LexA molecule LexA(1-202) as the DNA-binding region, instead of GAL4(1-147) or LexA(1-87). We find that, as in the original experiment, about 1% of the short peptides encoded by E. coli genomic fragments act as transcriptional activating regions when fused to intact LexA. All of the new activating regions whose sequences we determined bore an excess of acidic amino acids (see Table 1).