COMPARATIVE-ANALYSIS IN 3 FUNGI REVEALS STRUCTURALLY AND FUNCTIONALLYCONSERVED REGIONS IN THE MIG1 REPRESSOR

The Mig1 repressor is a key effector in glucose repression in the yeas t Saccharomyces cerevisiae. To gain further insights into structure-fu nction relationships, we have now cloned the MIG1 homologue from the y east Kluyveromyces marxianus. The amino acid sequence deduced from KmM IG1 differs significantly from ScMig1p outside the highly conserved zi nc fingers. However, 12 discrete conserved motifs could be identified in a multiple alignment that also included the K. lactis Mig1p sequenc e. We further found that KmMig1p is fully functional when expressed in S. cerevisiae. First, it represses the SUC2 promoter almost as well a s ScMig1p. This repression requires the Cyc8 and Tup1 proteins and is dependent on a C-terminal region comprising several conserved leucine- proline repeats. Second, KmMig1p is regulated by glucose in S. cerevis iae, and a KmMig1-VP16 hybrid activator is inhibited by the ScSnf1p ki nase in the absence of glucose. This suggests that KmMig1p has retaine d the ability to interact with several S. cerevisiae proteins, and rei nforces the notion that the conserved motifs are functionally importan t. Finally, we found that the physiological role of Mig1p also is cons erved in K. marxianus, since KmMig1p represses INU1, the counterpart o f SUC2 in this organism.