A mutant of Neurospora crassa deficient in cytochrome c heme lyase activity cannot import cytochrome c into mitochondria

The nuclear cyt-2-1 mutant of Neurospora crassa is characterized by
a gross deficiency of cytochrome c (Bertrand, H., and Collins, R.
A. (1978) Mol. Gen. Genet. 166, 1-13). The mutant produces mRNA
that can be translated into apocytochrome c in vitro. Apocytochrome
c is also synthesized in vivo in cyt-2-1, but it is rapidly
degraded and thus does not accumulate in the cytosol. Mitochondria
from wild-type cells bind apocytochrome c made in vitro from either
wild-type or cyt-2-1 mRNA and convert it to holocytochrome c. This
conversion depends on the addition of heme by cytochrome c heme
lyase and is coupled to translocation of cytochrome c into the
intermembrane space. Mitochondria from the cyt-2-1 strain are
deficient in the ability to bind apocytochrome c. They are also
completely devoid of cytochrome c heme lyase activity. These
defects explain the inability of the cyt-2-1 mutant to convert
apocytochrome c to the holo form and to import it into
mitochondria.