Cell cycle control of the yeast HO gene: cis- and trans-acting regulators.

In this paper, we investigate the role of a short repeated sequence (CACGA4) in the cell-cycle regulation of HO. We show that this sequence activates transcription of a heterologous gene in a cell-cycle-dependent fashion indistinguishable from that of the wild-type HO promoter. We also show that, in addition to SWI1 through SWI5, at least five other genes (SWI6 through SWI10) are required for HO transcription. These genes fit into three distinct classes with respect to their targets within the HO promoter. SWI4 and SWI6 are specifically required for CACGA4-mediated activation of transcription. SWI1, SWI2, and SWI5 are required for transcription from sequences physically separate from and independent of the CACGA4 sequences. SWI3 may be required for both. Since all the SWI genes are required for HO transcription, the HO promoter must contain at least two essential upstream activation sequences, which are affected by different trans-acting factors and are subject to different types of control.