Why is the "Show Enzymes" Button Missing for my DNA Sequence?
Many molecular biology softwares do not distinguish between single strand DNA (ssDNA) and double strand (dsDNA). SnapGene 5.2 and later represents ssDNA as a unique file type and allows the importing or creation of ssDNA sequences.
A ssDNA cannot be cut by restriction enzymes and as such the Show Enzymes button and some functionality accessed via menu Enzymes is disabled when viewing or editing a ssDNA sequence.
You can convert a ssDNA sequence to dsDNA sequence via menu Actions → Convert to Double Stranded. Once a ssDNA sequence is converted to dsDNA you will be able to see/use restriction sites. See the User Guide chapter on ssDNA for more information.