N-Acetylation, catalyzed with
N-acetyltransferase (NAT), is one of the most common co- and post-translational modifications of the α amino group of eukaryotic proteins. The eukaryotic 20S proteasome contains seven α-type and seven β-type subunits. We have found that the
N-terminus of α1, α2, α3, α4, α5, α6, α7, β3 and β4 subunits of yeast proteasome is acetylated with NAT. Experiments using the yeast NAT deletion mutant suggested that
N-acetylation be related to the proteolytic activity of the 20S proteasome (Kimura et al. J Biol Chem 2000; 275: 4635-9). In the present study, the rice 20S proteasome was purified by ion-exchange chromatography, gel filtration and glycerol density gradient centrifugation from the rice bran, and 14 subunits contained in the 20S proteasome were separated by two-dimensional electrophoresis and the partial amino acid sequence of them was analyzed by Edman degradation. The sequence analysis indicated that among 14 subunits, the α1, α2, α3, α4, α5, α6, α7, β3 and β4 subunits are
N-terminally blocked in rice as well as yeast, and besides these subunits, the β6 subunit is blocked in rice, but not in yeast. This suggests that the β6 subunit in rice may have different functions from that in yeast.
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