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 partia1 sequence of a regulatory subunit of the bovine 26s proteasome, p58 (C. 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] MOI Cen Cenet 251 : 11 46-1 521). I n our work, the expression of plant 21 D7 cDNA rescued the yeast sun2 mutant. Fractionation of carrot and spinach (Spinacia oleracea L.) crude extracts showed that the 21 D7 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 21 D7 protein sedimented together with the free regulatory complexes of the 26s proteasomes. Large-scale purification of carrot 26s proteasomes resulted i n coisolation of the 21 D 7 protein. Polyacrylamide gel electrophoresis under nondenaturing conditions showed that the 21 D7 protein had the same mobility as the 26s proteasome and that proteasome dissociation changed the mobility of the 21 D7 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.Most molecular studies of the cell division cycle in higher plants are based on the cloning of plant homologs of yeast and animal genes that control the cell cycle progression. However, in a number of cases the association of a gene with cell division has been shown first in a plant system (eg. Kodama et al., 1991;Ito and Komamine, 1993). In one of these cases, immunochemical studies of somatic embryogenesis resulted in the identification of a 45-kD carrot (Daucus carota L.) antigen, named 21D7 after the
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.