E. Mamroudkidron et C. Kahana, THE 26S PROTEASOME DEGRADES MOUSE AND YEAST ORNITHINE DECARBOXYLASE IN YEAST-CELLS, FEBS letters, 356(2-3), 1994, pp. 162-164
Eukaryotic cells possess two high-molecular-mass proteases, the 700 kD
a, 20S proteasome, as well as the even larger 1,400 kDa, 26S proteasom
e. It has been demonstrated that ornithine decarboxylase is degraded,
in vitro, by the 26S proteasome that contains the 20S protease as its
catalytic core, but not by the free 20S proteasome. Recently, by demon
strating severe inhibition of mouse and yeast ODC degradation in a mut
ant yeast cell line, defective in the chymotripsin-like activity of th
e yeast 20S proteasome, we implicated the 20S proteasome in the degrad
ation of ODC, in vivo, in yeast cells. Here we show that the degradati
on of ODC is also severely inhibited in the mutant yeast cell lines, c
im3-1 and cim5-1, containing a specific lesion in subunits that are un
ique to the yeast 26S proteasome. We therefore, conclude, that as illu
strated in vitro, also in intact cells, it is the 26S proteasome, not
the free 20S proteasome, that degrades ODC. We also demonstrate, that
while deficiency in the proteasome chymotrypsine-like activity (in the
yeast pre1-1 mutant) inhibits the degradation of both yeast and mouse
ODCs, deficiency in the peptidyl-glutamyl-peptide-hydrolyzing (PGPH)
activity inhibits only yeast ODC degradation. Similarly, we have noted
that whereas the putative ATPase activity of both the CIM3 and CIM5 s
ubunits is essential for the degradation of mouse ODC, only that of th
e CIM3 subunit is required for the degradation of yeast ODC. These res
ults suggest differential utilization of individual proteasomal subuni
ts in the recognition and degradation of individual short-lived protei
ns.