The nuclear Kluyveromyces lactis MRF1 gene encodes a mitochondrial class I peptide chain release factor that is important for cell viability

We report the isolation and characterization of the Kluyveromyces lactis MRF1 gene encoding mitochondrial peptide chain release factor mRF-1. Over-expression of the KlMRF1 gene has a strong antisuppressive effect in a Saccharomyces cerevisiae mitochondrial nonsense suppressor strain. Inactivation of KlMRF1 results in a dual phenotype: most cells die after about 10-13 generations, while a small number of cells exceed this limit. We propose that the lethality is related to a loss of mitochondrial genome integrity. Surviving Klmrf1 cells are able to grow slowly on the non-fermentable substrate glycerol, indicating the existence of a second mitochondrial release factor activity. Our previous comparative analysis of class I release factors is refined by the incorporation of KlmRF-1 and ten recently identified prokaryotic release factor sequences.Keywords Kluyveromyces lactis middle dot Mitochondrial release factor middle dot MRF1 middle dot Peptide chain termination