CHARACTERIZATION OF PROTEINS OF NUCLEAR ENVELOPES PREPARED FROM MUNG BEAN HYPOCOTYLS

The polypeptide composition of nuclear envelopes prepared from hypocot yls of mung bean (Vigna radiata) was investigated. The tissue was homo genized in the presence of Triton X-100 and nuclei were isolated by di fferential and discontinuous Percoll gradient centrifugation. The nucl ei were subjected to sonication in 2 M KCl or 50 mM lithium diiodosali cylate and then the nuclear envelopes were collected by centrifugation . Proteins in the envelope fraction were analyzed by sodium dodecylsul fate-polyacrylamide gel electrophoresis and blotting techniques. When the envelope fraction was incubated with [gamma-P-32]ATP, 10 to 15 pol ypeptides were labeled and the intensity of labeling of some of these polypeptides was enhanced by the addition of calcium ions. The results suggest the presence of a protein-phosphorylation system in nuclear e nvelopes. Three polypeptides of 100, 42, and 40 kDa stained blue with the cationic carbocyanine dye ''Stains-all'', and they were labeled wi th Ca-45(2+) on a transfer membrane. The lectin concanavalin A recogni zed glycoproteins that migrated as polypeptides of 50, 49, 47, 43, 35 and 32 kDa, respectively. Of these polypeptides the two larger ones we re prominent and were solubilized by treatment of the envelope fractio n with KCl at 2 M but not at less than 100 mM. These results suggest t hat the mung bean nuclear envelope contains some calcium-binding prote ins and glycoproteins. These newly identified proteins may become usef ul as characteristic markers of the nuclear envelope.