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Functional conservation of yeast mtTFB despite extensive sequence divergence

J A Carrodeguas1, S Yun, G S Shadel

  • 1Department of Pharmacological Sciences, State University of New York at Stony Brook, 11794-8651, USA.

Gene Expression
|January 1, 1996
PubMed

Insights

Mitochondrial transcription factor B (mtTFB) from Kluyveromyces lactis and Saccharomyces kluyveri were cloned and functionally characterized. These mtTFB proteins support yeast mitochondrial transcription initiation, despite low sequence identity with S. cerevisiae mtTFB.

Area of Science:

  • Mitochondrial genetics
  • Molecular biology
  • Yeast transcription

Background:

  • Mitochondrial transcription in Saccharomyces cerevisiae relies on mtRNA polymerase and a dissociable factor, mtTFB.
  • While mtTFB is characterized in S. cerevisiae, its detailed study in other yeasts is lacking.
  • Mitochondrial transcription in Kluyveromyces lactis uses the same promoter sequence as S. cerevisiae, but the involved proteins are uncharacterized.

Purpose of the Study:

  • To clone and characterize the mtTFB gene from Kluyveromyces lactis and Saccharomyces kluyveri.
  • To investigate the functional conservation and sequence divergence of mtTFB proteins across different yeast species.
  • To explore the mitochondrial import mechanisms of these mtTFB proteins.

Main Methods:

  • Cloning of mtTFB genes from K. lactis and S. kluyveri.
  • Heterologous expression of mtTFB proteins in E. coli and purification.
  • In vitro transcription assays using S. cerevisiae mtRNA polymerase.
  • Sequence alignment and analysis of mtTFB proteins.

Main Results:

  • Novel mtTFB genes from K. lactis and S. kluyveri were successfully cloned.
  • Both cloned mtTFB proteins functionally substituted for S. cerevisiae MTF1 and supported in vitro transcription.
  • K. lactis and S. kluyveri mtTFB proteins showed low sequence identity (40% and 56%, respectively) with S. cerevisiae mtTFB.
  • No highly conserved regions were identified, including putative bacterial sigma factor similarity domains.
  • All three yeast mtTFB genes lack canonical mitochondrial targeting sequences.

Conclusions:

  • mtTFB proteins from different yeast species can functionally substitute for each other, indicating conserved function despite sequence divergence.
  • The low sequence conservation suggests unique evolutionary paths for mtTFB in yeasts.
  • The absence of typical mitochondrial targeting sequences implies an unusual import pathway for these proteins into mitochondria.

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