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Short answer (first 60 words)
A restriction enzyme name index decodes endonuclease abbreviations into biological source, recognition sequence, cut coordinates, and reaction conditions under standard Roberts nomenclature. Based on bacterial genus, species, and strain identifiers, these designations determine critical bench choices: buffer compatibility, incubation temperatures, 5′ or 3′ overhang generation, and whether heat inactivation or column purification is required before downstream ligation.
Definition and scope
Restriction endonucleases are bacterial and archaeal enzymes that recognize specific double-stranded DNA sequences and catalyze phosphodiester bond cleavage. To prevent naming conflicts across thousands of restriction-modification systems, Roberts et al. (2003) established the international nomenclature standard in Nucleic Acids Research, indexed globally in REBASE.
Under this standard, each enzyme name provides a systematic code:
- Three-letter root: The first letter represents the bacterial genus (capitalized), followed by the first two letters of the species epithet in lowercase (e.g., Alu from Arthrobacter luteus, Apa from Acetobacter pasteurianus). Modern typographical rules do not require italicizing the enzyme acronym.
- Strain identifier: An unhyphenated character follows the species code when different strains yield distinct enzymes (e.g., “d” in HindIII).
- Roman numeral: Indicates the chronological order of isolation or characterization from that organism (e.g., SacI versus SacII).
- System prefixes: Standard notation prefixes “R.” for restriction endonucleases (e.g., R.EcoRI) and “M.” for cognate DNA methyltransferases (e.g., M.EcoRI).
How it works or how it is used in practice (from named sources)
Researchers consult an index before setting up restriction digests, reading plasmid maps, or constructing recombinant vectors. As documented by New England Biolabs technical references, endonucleases differ fundamentally by recognition architecture and cut geometry:
Standard Type IIP endonucleases recognize palindromic dyad symmetries and cut symmetrically, producing blunt ends or cohesive overhangs. Type IIS enzymes (such as SapI and SfaNI) recognize asymmetric non-palindromic sequences and cut at defined offsets outside their binding motif. This offset cleavage leaves cohesive ends that lack the recognition sequence, preventing vector re-cleavage during seamless assembly.
Using an index confirms compatibility with standard buffers—such as the recombinant albumin-formulated rCutSmart buffer—and identifies thermophilic enzymes (e.g., BsrI, active at 65°C) that require elevated incubation temperatures.
Types or related concepts (table only if every row is sourced)
The table below summarizes ten widely used restriction endonucleases, documenting source organism, recognition sequence, cleavage position, overhang type, incubation temperature, and validated heat inactivation conditions from primary New England Biolabs datasheets:
| Enzyme Name | Source Organism | Recognition Sequence (5′ to 3′) | Cleavage Pattern / Overhang | Incubation Temp (°C) | Heat Inactivation |
|---|---|---|---|---|---|
| AluI | Arthrobacter luteus | AG^CT | Blunt ends | 37°C | 80°C for 20 min |
| ApaI | Acetobacter pasteurianus | GGGCC^C | 4-nt 3′ overhang | 37°C | 65°C for 20 min |
| AsiSI | Anabaena species | GCGAT^CGC | 2-nt 3′ overhang | 37°C | 80°C for 20 min |
| BsrI | Bacillus stearothermophilus | ACTGG(1/-1)^ | 1-nt 5′ overhang | 65°C | 80°C for 20 min |
| MspI | Moraxella species | C^CGG | 2-nt 5′ overhang | 37°C | None (cannot be heat inactivated) |
| SacI | Streptomyces achromogenes | GAGCT^C | 4-nt 3′ overhang | 37°C | 65°C for 20 min |
| SapI | Saccharopolyspora species | GCTCTTC(1/4)^ | 3-nt 5′ overhang | 37°C | 65°C for 20 min |
| SfaNI | Streptococcus faecalis | GCATG(5/9)^ | 4-nt 5′ overhang | 37°C | 65°C for 20 min |
| SspI | Sphaerotilus species | AAT^ATT | Blunt ends | 37°C | 65°C for 20 min |
| StuI | Streptomyces tubercidicus | AGG^CCT | Blunt ends | 37°C | None (cannot be heat inactivated) |
Key biochemical attributes across these enzymes include:
- Shifted Type IIS cleavage: SfaNI cleaves 5 nucleotides downstream on the top strand and 9 on the bottom strand (5/9), leaving a 4-nt 5′ overhang. SapI cleaves 1 nucleotide downstream on top and 4 on bottom (1/4), yielding a 3-nt 5′ overhang for directional cloning.
- 3′ overhang generation: SacI and ApaI yield cohesive 3′ extensions. Modern ApaI lots containing recombinant albumin run at 37°C, superseding legacy 25°C protocols.
- Methylation sensitivity: MspI cleaves C^CGG even when the internal cytosine is methylated, contrasting with its isoschizomer HpaII, which CpG methylation blocks.
- Blunt cutters: AluI (4-bp target), SspI (6-bp target), and StuI (6-bp target) leave blunt ends. AluI and SspI can be heat inactivated, but StuI cannot.
- Thermophilic kinetics: BsrI originates from thermophilic Bacillus stearothermophilus and requires 65°C incubation.
- Rare genomic cleavage: AsiSI recognizes an 8-bp target (GCGAT^CGC), cleaving mammalian genomes infrequently for macro-restriction mapping.
Where it matters for labs, clinics or supply decisions (sourced)
Consulting an index prevents critical bench failures across molecular biology workflows:
- Heat denaturation versus column purification: Enzymes like SacI, SapI, SfaNI, and SspI denature at 65°C, while AluI, AsiSI, and BsrI require 80°C. In contrast, StuI and MspI resist heat inactivation; heating will not abolish activity, and reactions must undergo spin-column cleanup before ligation to avoid construct destruction.
- Double digestion in a multiple cloning site (MCS): Pairing endonucleases requires matching buffer salinity to prevent star activity (non-specific cleavage). Formulations like rCutSmart support over 200 enzymes in a single buffer, simplifying dual digests.
- Cloning strategy selection: Index data establishes whether overhangs are compatible for directional gene cloning, or whether assembly methods like Gibson assembly should be used to avoid restriction limitations entirely.
- Cross-referencing broader classes: When selecting alternative enzymes or isoschizomers, researchers refer to comprehensive reviews of restriction endonucleases to match methylation profiles and cleavage rates.
Common misunderstandings
- “All restriction enzymes can be heat-inactivated at 65°C.” Incorrect. Several enzymes require 80°C (AluI, AsiSI, BsrI), while StuI and MspI cannot be heat-inactivated at all. Applying heat to StuI leaves active enzyme that re-cuts vectors during ligation.
- “Isoschizomers always behave identically.” Isoschizomers share target sequences but can differ in cleavage positions (neoschizomers), optimal buffers, or methylation sensitivity (e.g., MspI versus HpaII).
- “Enzymes always cut within their recognition motif.” Type IIS enzymes (such as SapI and SfaNI) bind their specific recognition motif but cut double-stranded DNA outside of it, omitting the binding site from the insert.
- “Roman numerals represent enzyme subclass or strength.” The Roman numeral indicates the order of characterization from the host strain, not its mechanistic class or activity level.
Frequently asked questions
What do the letters in a restriction enzyme name mean?
The first capitalized letter represents the bacterial genus, followed by two lowercase letters denoting the species. Additional letters designate the strain, and a trailing Roman numeral marks the order of isolation from that organism.
How does SfaNI cut DNA?
SfaNI is a Type IIS enzyme recognizing 5′-GCATG-3′ that cleaves 5 nucleotides downstream on the top strand and 9 downstream on the bottom strand, producing a 4-nucleotide 5′ overhang.
Can StuI and MspI be heat-inactivated?
No. Neither StuI nor MspI can be heat-inactivated. Reaction mixtures containing them require spin-column cleanup or phenol extraction before subsequent ligation.
What is the difference between SacI and SapI?
SacI recognizes the palindromic 6-base sequence 5′-GAGCT^C-3′ and cleaves within it to generate a 4-nt 3′ overhang. SapI recognizes 5′-GCTCTTC(1/4)^-3′ and cleaves downstream to generate a 3-nt 5′ overhang.
Sources
- Roberts, R. J., Belfort, M., Bestor, T., Bhagwat, A. S., Bickle, T. A., Bitinaite, J., Blumenthal, R. M., Degtyarev, S. K., Dryden, D. T., Dybvig, K., et al. (2003). A nomenclature for restriction enzymes, DNA methyltransferases, homing endonucleases and their genes. Nucleic Acids Research, 31(7), 1805–1812. https://doi.org/10.1093/nar/gkg274 (Accessed 2026-11-07).
- New England Biolabs. (2026). Alphabetized List of Recognition Sequences and Restriction Endonucleases. https://www.neb.com/tools-and-resources/selection-tools/alphabetized-list-of-recognition-sequences (Accessed 2026-11-07).
- New England Biolabs. (2026). Enzyme Finder and Interactive Selection Tool. https://www.neb.com/en-us/tools-and-resources/interactive-tools/enzyme-finder (Accessed 2026-11-07).
- REBASE. (2026). The Restriction Enzyme Database. http://rebase.neb.com (Accessed 2026-11-07).
