PLANT PHYSIOLOGY , Vol 113, Issue 1 281-291, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Plant 21D7 Protein, a Nuclear Antigen Associated with Cell Division, Is a Component of the 26S Proteasome
M. W. Smith, M. Ito, M. Miyawaki, S. Sato, Y. Yoshikawa, S. Wada, H. Maki, H. Nakagawa and A. Komamine
Department of Chemical and Biological Sciences, Japan Women's University, Mejirodai 2-8-1, Bunkyo-ku, Tokyo 112, Japan (M.W.S., Y.Y., S.W., H.M., A.K.)
Previously, we cloned a carrot (Daucus carota L.) cDNA encoding a 45-kD
protein, 21D7, located in the nuclei of proliferating cells. The 21D7
protein is similar to the partial sequence of a regulatory subunit of the
bovine 26S proteasome, p58 (G. DeMartino, C.R. Moomaw, O.P. Zagnitko, R.J.
Proske, M. Chu-Ping, S.J. Afendis, J.C. Swaffield, C.A. Slaughter [1994] J
Biol Chem 269: 20878-20884) and to the deduced sequence encoded by the
Saccharomyces cerevisiae gene SUN2 (M. Kawamura, K. Kominami, J. Takeuchi,
A. Toh-e [1996] Mol Gen Genet 251: [146-152]). In our work, the expression
of plant 21D7 cDNA rescued the yeast sun2 mutant. Fractionation of carrot
and spinach (Spinacia oleracea L.) crude extracts showed that the 21D7
protein sedimented with the active 26S proteasomes. The cessation of cell
proliferation in carrot suspensions at the stationary phase caused 26S
proteasome dissociation and, correspondingly, the 21D7 protein sedimented
together with the free regulatory complexes of the 26S proteasomes.
Large-scale purification of carrot 26S proteasomes resulted in coisolation
of the 21D7 protein. Polyacrylamide gel electrophoresis under nondenaturing
conditions showed that the 21D7 protein had the same mobility as the 26S
proteasome and that proteasome dissociation changed the mobility of the
21D7 protein accordingly. We conclude that the 21D7 protein is a subunit of
the plant 26S proteasome and that it probably belongs to the proteasome
regulatory complex.
