Functional conservation of yeast mtTFB despite extensive sequence divergence

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.