DNA binding and uptake by nuclei isolated from plant protoplasts: factors affecting DNA binding and uptake

DNA binding and uptake by nuclei isolated from soybean (Glycine max L. Merr.) protoplasts were investigated using radioactive homogeneous DNA prepared from soybean cells. DNA binding to nuclei was found to decrease drastically with increased incubation time. Total uptake and acid-precipitable uptake reached a maximum after 20 minutes of incubation. Optimum DNA binding and uptake occurred at pH 6 and the process was enhanced by increasing the incubation temperature to 40 C. Salmonella typhimurium DNA and poly ([dA-dT]-[dA-dT]) competitively inhibited DNA binding whereas calf thymus DNA was less competitive; however, Micrococcus lysodeikticus DNA stimulated DNA binding and tobacco mosaic virus RNA had no effect. DNA binding and uptake was enhanced by addition of Mg ions, Ca ions, poly-l-lysine, and ATP. Increasing amounts of EDTA appeared to decrease DNA binding. Pronase strongly inhibited DNA binding and uptake.