Electroporation of cells with restriction endonucleases. Synchronized normal human diploid cells in G1 were collected by trypsinization and suspended in PBS buffer. Enzyme reaction buffer and Pvu II (100 U) were mixed immediately before electroporation as described in METHODS. Cells were incubated for 2 hours before fixation. Control; no treatment, Buffer; cells were electroporated with reaction buffer, Pvu II; cells were treated with 100 U of Pvu II, HS Pvu II, cells were electroporated with Pvu II (100 U) heat inactivated at 80°C for 20 minutes.