Je. Azevedo et al., CLONING, IN-VITRO MITOCHONDRIAL IMPORT AND MEMBRANE ASSEMBLY OF THE 17.8 KDA SUBUNIT OF COMPLEX-I FROM NEUROSPORA-CRASSA, Biochemical journal, 293, 1993, pp. 501-506
We have cloned and sequenced a cDNA encoding a 17.8 kDa subunit of the
hydrophobic fragment of complex I from Neurospora crassa. The deduced
primary structure of this subunit was partially confirmed by automate
d Edman degradation of the isolated polypeptide. The sequence data obt
ained indicate that the 17.8 kDa subunit is made as an extended precur
sor of 20.8 kDa. Resistance of the polypeptide to alkaline extraction
from mitochondrial membranes and the existence of a putative membrane-
spanning domain suggests that the 17.8 kDa subunit is an intrinsic (bi
topic) membrane protein. The in vitro synthesized precursor of the 17.
8 kDa subunit can be efficiently imported into isolated mitochondria,
where it is cleaved to the mature species by the metal-dependent matri
x-processing peptidase. The in vitro imported mature subunit is found
mainly exposed to the mitochondrial intermembrane space. However, a si
gnificant fraction of the imported polypeptide acquires the same membr
ane topology as the endogenous subunit, indicating that correct assemb
ly in the mitochondrial inner membrane did occur.