Deletion of QCR6, the gene encoding subunit six of the mitochondrial cytochrome bc1 complex, blocks maturation of cytochrome c1, and causes temperature-sensitive petite growth in Saccharomyces cerevisiae.
It was previously reported that disruption or deletion of QCR6, the nuclear gene encoding subunit 6 of the cytochrome bc1 complex, does not impair growth of yeast on non-fermentable carbon sources (Schoppink, P. J., Hemrika, W., Reyne, J. M., Grivell, L.A., and Berden, J. A. (1988) Eur. J. Biochem. 113, 115-122; Crivellone, M. D., Wu, M. M., and Tzagoloff, A. (1988) J. Biol. Chem. 262, 14323-14333; Schmitt, M. E., and Trumpower, B. L. (1990) J. Biol. Chem. 265, 17005-17011). We have discovered that deletion of QCR6 results in a temperature-sensitive petite phenotype, manifested at 37 degrees C, and that this phenotype can be masked by spontaneously arising suppressor mutations. Mitochondrial membranes from the deletion strain grown at 37 degrees C lack ubiquinol-cytochrome c reductase activity, and optical spectra reveal an extensive decrease in cytochrome b absorption, but little or no decrease in cytochrome c1 absorption. Immunoblots of mitochondrial membrane proteins from the deletion strain indicate that processing of cytochrome c1 from intermediate to mature size is blocked coincident with the loss of subunit 6. This is the first example where mutation of a subunit within the bc1 complex blocks maturation of cytochrome c1.
Yang
M
M
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755.
Trumpower
B L
BL
D003575:Cytochromes c1 / Q000378:metabolism*; D014450:Electron Transport Complex III / Q000235:genetics*; D017353:Gene Deletion; D005800:Genes, Fungal; D016153:Genes, Suppressor; D007425:Intracellular Membranes / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology*; D009245:NADH Dehydrogenase / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D013696:Temperature
D003575:Cytochromes c1; D009245:NADH Dehydrogenase; D014450:Electron Transport Complex III