UAS(MAG1), a yeast cis-acting element that regulates the expression of MAG1, is located within the protein coding region of DDI1.

MAG1 and DDI1 are two divergently transcribed DNA damage-inducible genes from Saccharomyces cerevisiae. Previous studies have shown that MAG1 induction requires an upstream activating site (UAS) located between nucleotides -376 and -330. Here we show that a 24-bp oligonucleotide from within the UAS(MAG1) region forms a sequence-specific DNA-protein complex with partially purified proteins from S. cerevisiae. Point mutations introduced into the 24-bp oligonucleotide inhibited the formation of the DNA-protein complex and decreased the level of induction of MAG1-lacZ. By determining the transcription and translation start points of both MAG1 and DDI1, an interesting, indeed unprecedented feature of genome organization in eukaryotes was revealed: UAS(MAG1) actually lies within the protein-coding region of DDI1. Although tightly linked to each other, and co-induced upon treatment with DNA-damaging agents, DDI1 does not share the UAS(MAG1) required for DNA damage induction of MAG1. Furthermore, MAG1 and DDI1 respond differently in the presence of the protein synthesis inhibitor cycloheximide, suggesting that these two genes are regulated by different mechanisms in the absence of de novo protein synthesis.