A restriction enzyme recognizes a short palindromic sequence and cuts the circular plasmid at that site, leaving "sticky ends." DNA ligase then splices a foreign gene insert into the gap, producing recombinant DNA. Once the plasmid re-enters (transforms) a bacterial cell, its promoter drives transcription and translation of the inserted gene into protein, which accumulates as the cell divides.
Transformation efficiency = colonies / µg DNA
Expression rate ∝ promoter strength × plasmid copy number
Yield(t) = Yield(t-1) + k·strength·copies·dt
- Gene insert — selects which foreign gene (GFP, insulin, Bt toxin) is spliced into the plasmid, changing the produced protein and cut-site geometry.
- Restriction enzyme efficiency — probability the cut-and-paste (ligation) step succeeds per cycle; low efficiency stalls the plasmid at "cut, unligated."
- Promoter strength — scales how fast the transformed cell transcribes/translates the insert into visible protein particles.
- Play/Step — runs the cut→splice→transform→express cycle continuously or one stage at a time.
This is the core workflow behind producing recombinant human insulin in E. coli, still the standard industrial method today.