Cell differentiation by interaction of two HMG-box proteins: Mat1-Mc activates M cell-specific genes in S.pombe by recruiting the ubiquitous transcription factor Ste11 to weak binding sites.
The Schizosaccharomyces pombe mfm1 gene is expressed in an M cell-specific fashion. This regulation requires two HMG-box proteins: the ubiquitous Ste11 transcription factor and the M cell-controlling protein Mat1-Mc. Here we report that the mfm1 promoter contains a single, weak Stell-binding site (a so-called TR-box) that can confer M-specificity on a heterologous promoter when present in eight copies. In vitro, both Mat1-Mc and Ste11 can bind this box with approximately the same affinity. The Mat1-Mc protein caused a dramatic increase in the DNA-binding of Ste11 to this box, under conditions where we could not detect Mat1-Mc in the resulting protein-DNA complex. When we changed a single base in the mfm1 TR-box, such that it resembled those boxes found in ubiquitously expressed genes, Ste11 binding was enhanced, and in vivo the mfm1 gene also became expressed in P cells where Mat1-Mc is absent. These findings suggest that M-specificity results from Mat1-Mc-mediated Ste11 binding to weak TR-boxes. We have also defined a novel motif (termed M-box), adjacent to the mfm1 TR-box, to which Mat1-Mc binds strongly. A DNA fragment containing both the TR- and the M-box allowed the formation of a complex containing both Ste11 and Mat1-Mc. A single copy of this fragment was sufficient to activate a heterologous promoter in an M-specific fashion, suggesting that these two boxes act in a synergistic manner.
Kjaerulff
S
S
Department of Genetics, Institute of Molecular Biology, University of Copenhagen, Copenhagen K, Denmark.
Dooijes
D
D
Clevers
H
H
Nielsen
O
O
D001483:Base Sequence; D001665:Binding Sites; D002454:Cell Differentiation / Q000235:genetics; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D003850:Deoxyribonuclease I / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D036341:Intercellular Signaling Peptides and Proteins; D008938:Mitosis; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors / Q000378:metabolism*
D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D036341:Intercellular Signaling Peptides and Proteins; C089516:Mating Factor, S pombe; D010455:Peptides; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C490320:mfm1 protein, S pombe; C071596:ste11 protein, S pombe; D003850:Deoxyribonuclease I