Roles of the TGACT repeat sequence in the yeast TRP5 promoter

Yeast genes under general amino acid control contain multiple copies of a sequence known as the TGACT repeat in the 5'-flanking DNA. The yeast TRP5 gene contains two copies of the TGACT repeat sequence in its 5'-flanking region. The upstream TGACT repeat of TRP5 is required for normal basal expression as well as derepression by general control. Synthetic oligonucleotides containing a TGACT sequence were inserted into previously constructed TRP5 control region deletion mutants. A synthetic 17-base pairs (bp) oligonucleotide containing a TGACT copy along with flanking nucleotides from HIS3 was able to restore derepression in all deletion mutants tested. The 17-bp oligonucleotide also functioned bidirectionally. Replacements in the upstream control region by synthetic oligonucleotides indicated that sequences other than the TGACT repeat are required for high basal expression. Replacements of the downstream repeat sequence by the 17-bp oligonucleotide suggest its main role in this position is for derepressed expression. High level derepressed expression was found to correlate with the presence of two repeats.