A Saccharomyces cerevisiae mitochondrial transcription factor, sc-mtTFB, shares features with sigma factors but is functionally distinct.
In Saccharomyces cerevisiae mitochondria, sc-mtTFB is a 341-amino-acid transcription factor required for initiation of transcription from mitochondrial DNA promoters. Specific transcription in vitro requires only sc-mtTFB and the bacteriophage-related core sc-mtRNA polymerase. Mutational analysis of sc-mtTFB has defined two regions of the protein that are important for normal function both in vivo and in vitro. These regions overlap portions of the protein that exhibit similarity to conserved region 2 of bacterial sigma factors. One mutation in this region of sc-mtTFB (tyrosine 108 to arginine [Y108R]) has a defective phenotype that matches that observed for mutations in the corresponding residue of Bacillus subtilis sigma A and sigma E proteins. However, mutations in the sigma 2.4-like region, including a 5-amino-acid deletion corresponding to crucial promoter-contacting amino acids of sigma factors, did not eliminate the ability of sc-mtTFB to initiate transcription specifically in vitro. This suggests a mechanism of promoter recognition for sc-mtRNA polymerase different from that used by bacterial RNA polymerases. Two mutations in a basic region of sc-mtTFB resulted in defective proteins that were virtually dependent on supercoiled DNA templates in vitro. These mutations may have disrupted a DNA-unwinding function of sc-mtTFB that is only manifested in vitro and is partially rescued by DNA supercoiling.
Shadel
G S
GS
Department of Developmental Biology, Stanford University School of Medicine, California 94305-5427.
Clayton
D A
DA
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004252:DNA Mutational Analysis; D004278:DNA, Superhelical; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D010641:Phenotype; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D004278:DNA, Superhelical; D005656:Fungal Proteins; C071720:MTF1 protein, S cerevisiae; D024101:Mitochondrial Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D012808:Sigma Factor; D014157:Transcription Factors; D012321:DNA-Directed RNA Polymerases