Association of the cell cycle transcription factor Mbp1 with the Skn7 response regulator in budding yeast

We previously isolated the SKN7 gene in a screen designed to isolate new co mponents of the G1-S cell cycle transcription machinery in budding yeast. W e have now found that Skn7 associates with Mbp1, the DNA-binding component of the G1-S transcription factor DSC1/MBF. SKN7 and MBP1 show several genet ic interactions. Skn7 overexpression is lethal and is suppressed by a mutat ion in MBP1. Similarly, high overexpression of Mbp1 is lethal and can be su ppressed by skn7 mutations. SKN7 is also required for MBP1 function in a mu tant compromised for G1-specific transcription. Gel-retardation assays indi cate that Skn7 is not an integral part of MBF. However, a physical interact ion between Skn7 and Mbp1 was detected using two-hybrid assays and GST pull downs. Thus, Skn7 and Mbp1 seem to form a transcription factor independent of MBF. Genetic data suggest that this new transcription factor could be in volved in the bud-emergence process.