Homothallic yeast cells undergo a specific pattern of mating-type switching initiated by an endonuclease encoded by the HO gene. HO transcription is affected by cell type (a, alpha, and a/alpha), by cell age (mother or daughter), and by the cell cycle. This paper investigates the sequences involved in HO transcription by replacing genomic DNA with copies mutated in vitro. A region between -1000 and 1400 (called URS1) is necessary for transcription in addition to a XTATAX-like region at -90. The 900 bp of DNA separating URS1 from the XTATAX box is not necessary for transcription nor for a/alpha repression and some measure of mother/daughter control, but it is necessary for correct cell cycle control.