H. Fang et al., THE HOMOLOG OF MAMMALIAN SPC12 IS IMPORTANT FOR EFFICIENT SIGNAL PEPTIDASE ACTIVITY IN SACCHAROMYCES-CEREVISIAE, The Journal of biological chemistry, 271(28), 1996, pp. 16460-16465
The multisubunit signal peptidase catalyzes the cleavage of signal pep
tides and the degradation of some membrane proteins within the endopla
smic reticulum (ER). The only subunit of this enzyme functionally exam
ined to date, yeast Sec11p, is related to signal peptidase I from bact
eria. Since bacterial signal peptidase is capable of processing both p
rokaryotic and eukaryotic signal sequences as a monomer, it is unclear
why the analogous enzyme in the ER contains proteins unrelated to sig
nal peptidase I. To address this issue, the gene encoding Spc1p, the y
east homologue to mammalian SPC12, is isolated from the yeast Saccharo
myces cerevisiae, Spc1p co-purifies and genetically interacts with Sec
11p, but unlike Sec11p, Spc1p is not required for cell growth or the p
roteolytic processing of tested proteins in yeast, This indicates that
only a subset of the ER signal peptidase subunits is required for sig
nal peptidase and protein degradation activities in vivo. Through both
genetic and biochemical criteria. Spc1p appears, however, to be impor
tant for efficient signal peptidase activity.