Abstract
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.
Highlights
It was previously reported that disruptiondeloertion and sequenced, and theQCR6-encoded protein wasfound to be of QCR6, the nuclear gene encoding subunit 6 of the 37% similar t o the acidic hinge protein of the bovine bcl cytochrome bcl complex,doesnotimpairgrowthof complex (8).The hinge protein associates with cytochrome c1 yeast on non-fermentable carbon sources
Purified yeast mitochondrial cytochrome bcl complex consists of at least nine polypeptide subunits.' Three of the subunits contain prosthetic groups, cytochrome cl, cytochrome b, and Rieske iron-sulfur protein and are obligatory for the electron transfer andenergy transducing reactions of the complex (1).Purified bcl complexes from numerous bacteria consist of only the three redox prosthetic group containing subunits (25), and these bacterial complexes appear to be functionally equivalent to themitochondrial complexes (5,6)
The deletion strain grew on non-fermentable carbon sources, and a stable bcl complex lacking subunit 6 could be purified from the mitochondrial membranes (13).Both the first-order rate constant and the zeroorderrate of ubiquinol-cytochrome c reductase activity of mitochondrial membranes from the deletion strain were reversibly reduced to 50%of those in the parental strainO.n the basis of this observation, we postulated that subunit 6 regulates cytochrome c reductase activity of the bcl complex, revers
Summary
It was previously reported that disruptiondeloertion and sequenced, and theQCR6-encoded protein wasfound to be of QCR6, the nuclear gene encoding subunit 6 of the 37% similar t o the acidic hinge protein of the bovine bcl cytochrome bcl complex,doesnotimpairgrowthof complex (8).The hinge protein associates with cytochrome c1 yeast on non-fermentable carbon sources Afew micro- LEU2 gene as a selectablemarker,tetrad spores werealso grams of the DNA were digested with SphI, separatedon an 0.8 % agarose gel, and transferred to nitrocellulose membraneTs.he blot was probed with the labeled 1.9-kilobase pair SphI fragment isolated from pMES2,whichcontains the QCR6 reading frame and flanking sequences (13).
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