Restriction Enzyme Calculator

Restriction enzyme (RE) cloning uses endonucleases that recognize and digest DNA at specific short sequences (typically 4-8 base pairs). Each enzyme produces a predictable cut pattern, leaving either sticky ends (single-stranded overhangs) or blunt ends.

The standard workflow: digest the vector backbone with one or two restriction enzymes, digest the insert with the same enzymes, then ligate the compatible fragments with DNA ligase. When two different enzymes are used, the non-complementary overhangs force the insert into a single orientation — this is directional cloning, and it is the standard approach for most recombinant DNA work.

RE cloning is the simplest conceptual approach to molecular cloning. If convenient unique restriction sites exist in both the backbone and insert, RE cloning is typically faster than overlap-based methods like Gibson Assembly. The calculator above identifies these compatible enzyme pairs automatically.

The ideal enzyme pair for directional cloning satisfies three criteria: each enzyme is a unique cutter in the backbone (cuts exactly once), each enzyme is a non-cutter in the insert (zero cuts), and the two enzymes produce different overhangs (preventing self-ligation and ensuring correct insert orientation).

Beyond the basic compatibility check, consider these practical factors:

• Buffer compatibility — enzymes in a double digest must work efficiently in the same buffer. Most high-fidelity (HF) variants from NEB work in rCutsmart buffer.
• Overhang type — 5′ overhangs (like EcoRI and BamHI) ligate more efficiently than 3′ overhangs or blunt ends.
• Methylation sensitivity — some enzymes are blocked by Dam or Dcm methylation. Check the methylation section below.
• Recognition length — 6-base cutters are the standard for cloning. 4-base cutters produce too many fragments; 8-base cutters are rare enzymes with limited availability.

Agarose gel electrophoresis separates DNA fragments by size. Smaller fragments migrate further from the well, following a roughly log-linear relationship with molecular weight. A DNA ladder in the first lane provides size reference markers.

For a diagnostic restriction digest, you expect to see: an uncut control lane showing a single band (or multiple conformations for supercoiled plasmid), and a digest lane showing the expected fragments. The gel simulation above shows the predicted pattern for your enzyme selection.

Band brightness is proportional to fragment mass — larger fragments bind more ethidium bromide (EtBr) and appear brighter. Very small fragments (<100 bp) may run off the gel or be too faint to see. If your digest produces fragments that differ by less than ~10% in size, they may co-migrate and appear as a single bright band.

Real gels may show additional bands from partial digestion, nicked DNA, or concatamers that are not represented in the simulation.

E. coli expresses two DNA methyltransferases that modify specific motifs: Dam methylates adenine in GATC sequences, and Dcm methylates cytosine in CC(A/T)GG sequences. DNA propagated in standard laboratory E. coli strains carries both modifications.

Some restriction enzymes are partially or completely blocked by methylation at or near their recognition sites. When this calculator flags a methylation warning, the enzyme may fail to digest DNA isolated from standard E. coli strains.

Practical solutions:

• Use a dam⁻/dcm⁻ strain — strains like JM110 or SCS110 lack both methyltransferases, producing unmethylated DNA.
• Use an isoschizomer — enzymes that recognize the same sequence but differ in methylation sensitivity. For example, DpnII is methylation-insensitive and recognizes GATC like MboI.
• Use PCR-amplified DNA — PCR products lack methylation, so methylation-sensitive enzymes will digest them normally.

Each cloning method has a natural domain where it excels:

A practical rule of thumb: if this calculator finds a compatible enzyme pair with 5′ overhangs, RE cloning is likely the fastest path. If no convenient sites exist, consider Gibson Assembly. For multi-part combinatorial work (promoter libraries, pathway engineering), Golden Gate is the standard.

PlasmidStudio's Cloning Strategy Advisor analyzes your construct and recommends the optimal method automatically.