Yeast mitochondria lacking the two import receptors Mas20p and Mas70p can efficiently and specifically import precursor proteins.
Mas20p and Mas70p are integral proteins of the yeast mitochondrial outer membrane that appear to function as receptors for precursor proteins imported from the cytosol. Loss of either receptor alone does not block import or kill the cells, but deletion of Mas20p causes loss of respiration (Ramage, L., Junne, T., Hahne, K., Lithgow, T., and Schatz, G. (1993) EMBO J. 12, 4115-4123). Here we show that this respiratory deficiency is only temporary; given time to adapt, virtually all cells lacking MAS20p regain respiration without regaining MAS20p. The respiratory defect can also be suppressed (at a frequency of about 10(-6)) by a dominant mutation of a single nuclear gene. The suppressed cells, unlike the unsuppressed ones, tolerate disruption of the MAS70 gene. The resulting double disruptants lack both Mas20p and Mas70p, yet are viable and able to respire. Protein import into mitochondria isolated from these cells is efficient, specific, and highly sensitive to protease treatment. We propose that at least one additional mitochondrial surface protein can function as a protein import receptor and that the activity of this component is up-regulated by a stress response or by an extragenic suppressor.
Lithgow
T
T
Biozentrum, University of Basel, Switzerland.
Junne
T
T
Wachter
C
C
Schatz
G
G
D001692:Biological Transport; D003575:Cytochromes c1 / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D042844:L-Lactate Dehydrogenase (Cytochrome); D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D010100:Oxygen / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011498:Protein Precursors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae; C489039:TOM70 protein, S cerevisiae; D003575:Cytochromes c1; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); D010100:Oxygen