Plasmids can be constructed without restriction enzymes using Gateway cloning, which inserts DNA fragments by recombination. SnapGene simulates different variations of this method.
For standard Gateway cloning, a DNA fragment is inserted into a Donor Vector in a BP cloning reaction, creating an Entry Vector. Then the fragment is transferred to a Destination Vector in an LR cloning reaction, creating the final Expression Vector. Multisite Gateway cloning allows up to four fragments to be inserted simultaneously.