Functional and physical interactions within the middle domain of the yeast mediator.
Med21 (Srb7) is a small essential subunit of the middle domain of the Mediator, which is conserved in all eukaryotes. It is thought to play an important role in both transcriptional activation and repression. In the yeast Saccharomyces cerevisiae, Med21 is known to interact both with the Mediator subunit Med6 and the global co-repressor Tup1. We have made a temperature-sensitive med21-ts mutant, which we used in a high copy number suppressor screen. We found ten yeast genes that can suppress the med21-ts mutation in high copy number. The three strongest suppressors were MED7 and MED10 (NUT2), which encode other Mediator subunits, and ASH1, which encodes a repressor of the HO gene. 2-Hybrid experiments confirmed multiple interactions between Med21, Med10, Med7 and Med4, and also revealed a Med21 self-interaction. The interactions of Med21 with Med7 and Med10 were verified by co-immunoprecipitation of tagged proteins produced in insect cells and E. coli, where both interactions were found to depend strongly on the amino acid residues 2-8 of Med21. These interactions, and the interactions of Med21 with Med6 and Tup1, suggest that Med21 may serve as a molecular switchboard that integrates different signals before they reach the core polymerase.
Hallberg
Magnus
M
Department of Medical Biochemistry and Biophysics, Umeå University, 0187, Umeå, Sweden.
Hu
Guo-Zhen
GZ
Tronnersjö
Susanna
S
Adler
David
D
Balciunas
Darius
D
Björklund
Stefan
S
Ronne
Hans
H
D000595:Amino Acid Sequence; D015966:Gene Expression Regulation, Fungal / Q000235:genetics*; D056892:Mediator Complex; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics*; D020798:Two-Hybrid System Techniques
C110184:MED7 protein, S cerevisiae; D056892:Mediator Complex; D046912:Multiprotein Complexes; C113770:NUT2 protein, S cerevisiae; D009687:Nuclear Proteins; C093965:SRB7 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors