Volume 272, Number 4,
Issue of January 24, 1997
pp. 2212-2217
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Two-step Processing Is Not Essential for the Import and Assembly
of Functionally Active Iron-Sulfur Protein into the Cytochrome
bc1 Complex in Saccharomyces
cerevisiae
(Received for publication, July 22, 1996, and in revised form, November 7, 1996)
Jürgen H.
Nett
,
Elke
Denke
and
Bernard L.
Trumpower
From the Department of Biochemistry, Dartmouth Medical School,
Hanover, New Hampshire 03755
The iron-sulfur protein of the cytochrome
bc1 complex is one of a small number of
proteins that are processed in two sequential steps by matrix
processing peptidase (MPP) and mitochondrial intermediate peptidase
(MIP) during import into Saccharomyces cerevisiae
mitochondria. To test whether two-step processing is necessary for
import and assembly of the iron-sulfur protein into the cytochrome
bc1 complex, we mutagenized the presequence of
the iron-sulfur protein to eliminate the original MPP site and replace
the MIP site with a new MPP site. The mutated presequence is cleaved
and forms mature-sized protein in a single step, and the mature-sized
iron-sulfur protein is correctly targeted to the outer side of the
inner mitochondrial membrane in vitro.
Mutant iron-sulfur protein which is processed to mature size in one
step complements the respiratory deficient phenotype of a yeast strain
in which the endogenous gene for the iron-sulfur protein is deleted.
These results establish that mature-sized iron-sulfur protein can be
formed by single-step processing and assembled into a functionally
active form in the cytochrome bc1 complex in
S. cerevisiae.