Transcription of the HO gene in the yeast S. cerevisiae is subject to three separate types of control. Transcription is repressed in diploids, (a/d repression); it is activated in haploids, but only those which have undergone cell division (mother cells). Finally, activation of HO transcription is restricted to the late GI phase of the cell cycle (cell cycle control). UAS elements in distinct upstream regulatory regions (URS) mediate mother/daughter control (URSI) and cell cycle control (URS2). These UAS elements can act automonously to activate HO transcription when they are physically separated from each other. However, within the context of the HO promoter, neither UAS is sufficient to activate transcription. Deletions which remove URSI from the HO promoter prevent HO transcription. In addition, mutations in either of two regulatory proteins which specifically mediate transcription from the UAS in URS2 also eliminate HO transcription. Such results imply the existence of an additional negative control region within the intact promoter whose action is only overcome when both URSI and URS2 are active. The experiments in this research planning grant are designed to genetically identify and characterize the sites and trans-acting factors involved in this negative control.
