An expression cassette is a distinct component of vector DNA consisting of a gene and regulatory sequence to be expressed by a transfected cell.
[1] In each successful transformation, the expression cassette directs the cell's machinery to make RNA and protein(s).
Some expression cassettes are designed for modular cloning of protein-encoding sequences so that the same cassette can easily be altered to make different proteins.
[3] An expression cassette comprises three components: a promoter sequence, an open reading frame, and a 3' untranslated region that, in eukaryotes, usually contains a polyadenylation site.
[4] Different expression cassettes can be transfected into different organisms including bacteria, yeast, plants, and mammalian cells as long as the correct regulatory sequences are used.