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Mol. Cell. Biol., Apr 1995, 2101-2108, Vol 15, No. 4
GS Shadel and DA Clayton
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.
Copyright © 1995, American Society for Microbiology
A Saccharomyces cerevisiae mitochondrial transcription factor, sc- mtTFB, shares features with sigma factors but is functionally distinct
Department of Developmental Biology, Stanford University School of Medicine, California 94305-5427.
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