bio-restriction-sites

What this skill does

## Version Compatibility

Reference examples tested with: BioPython 1.83+

Before using code patterns, verify installed versions match. If versions differ:
- Python: `pip show <package>` then `help(module.function)` to check signatures

If code throws ImportError, AttributeError, or TypeError, introspect the installed
package and adapt the example to match the actual API rather than retrying.

# Finding Restriction Sites

**"Find restriction sites in my DNA sequence"** -> Locate cut positions for one or more restriction enzymes in linear or circular DNA.
- Python: `Bio.Restriction.Analysis(rb, seq, linear=True).full()`

## Core Pattern

```python
from Bio import SeqIO
from Bio.Restriction import EcoRI, BamHI, HindIII, RestrictionBatch, Analysis

record = SeqIO.read('sequence.fasta', 'fasta')
seq = record.seq

# Single enzyme
sites = EcoRI.search(seq)  # Returns list of cut positions
```

## Search with Single Enzyme

```python
from Bio.Restriction import EcoRI

sites = EcoRI.search(seq)
print(f'EcoRI cuts at positions: {sites}')
print(f'Number of sites: {len(sites)}')

# Check if enzyme cuts
if EcoRI.search(seq):
    print('EcoRI cuts this sequence')
else:
    print('EcoRI does not cut')
```

## Search with Multiple Enzymes

```python
from Bio.Restriction import RestrictionBatch, EcoRI, BamHI, HindIII, XhoI

batch = RestrictionBatch([EcoRI, BamHI, HindIII, XhoI])

# Method 1: batch.search()
results = batch.search(seq)
for enzyme, sites in results.items():
    if sites:
        print(f'{enzyme}: {sites}')

# Method 2: Analysis class
analysis = Analysis(batch, seq)
results = analysis.full()
```

## Use Built-in Enzyme Collections

```python
from Bio.Restriction import AllEnzymes, CommOnly

# All known enzymes (800+)
analysis = Analysis(AllEnzymes, seq)

# Commercially available only
analysis = Analysis(CommOnly, seq)

# Get results
results = analysis.full()
for enzyme, sites in results.items():
    if sites:
        print(f'{enzyme}: {sites}')
```

## Linear vs Circular DNA

```python
from Bio.Restriction import EcoRI, Analysis, RestrictionBatch

# Linear DNA (default)
sites_linear = EcoRI.search(seq, linear=True)

# Circular DNA (plasmid)
sites_circular = EcoRI.search(seq, linear=False)

# With Analysis class
batch = RestrictionBatch([EcoRI, BamHI])
analysis = Analysis(batch, seq, linear=False)  # Circular
```

## Filter Results

```python
from Bio.Restriction import Analysis, CommOnly

analysis = Analysis(CommOnly, seq)

# Only enzymes that cut
analysis.print_that_cut()

# Only enzymes that don't cut (non-cutters)
analysis.print_that_dont_cut()

# Enzymes that cut once
analysis.print_once_cutters()

# Enzymes that cut twice
analysis.print_twice_cutters()

# Get as dictionary
cutters = analysis.only_cut()
non_cutters = analysis.only_dont_cut()
once_cutters = analysis.once_cutters()
twice_cutters = analysis.twice_cutters()
```

## Get Enzyme Information

```python
from Bio.Restriction import EcoRI

# Recognition sequence
print(f'Site: {EcoRI.site}')           # GAATTC
print(f'Esite: {EcoRI.esite}')         # Recognition with cut position

# Cut characteristics
print(f'Overhang: {EcoRI.ovhg}')       # 4 (positive = 5' overhang)
print(f'Blunt: {EcoRI.is_blunt()}')    # False
print(f'5\' overhang: {EcoRI.is_5overhang()}')  # True
print(f'3\' overhang: {EcoRI.is_3overhang()}')  # False

# Overhang sequence
print(f'Overhang seq: {EcoRI.ovhgseq}')  # AATT

# Isoschizomers (same recognition, different cut)
print(f'Isoschizomers: {EcoRI.isoschizomers()}')

# Compatible enzymes (same overhang)
print(f'Compatible: {EcoRI.compatible_end()}')
```

## Common Cloning Enzymes

```python
from Bio.Restriction import (
    EcoRI, BamHI, HindIII, XhoI, SalI, NotI, XbaI, SpeI,
    NcoI, NdeI, BglII, PstI, KpnI, SacI, EcoRV, SmaI
)

common_enzymes = RestrictionBatch([
    EcoRI, BamHI, HindIII, XhoI, SalI, NotI, XbaI,
    NcoI, NdeI, BglII, PstI, KpnI, SacI, EcoRV, SmaI
])

analysis = Analysis(common_enzymes, seq)
results = analysis.full()
```

## Access Enzymes by Name

```python
from Bio.Restriction import AllEnzymes

# Get enzyme by string name
ecori = AllEnzymes.get('EcoRI')
sites = ecori.search(seq)

# Check if enzyme exists
if 'EcoRI' in AllEnzymes:
    print('EcoRI is in database')
```

## Search Multiple Sequences

```python
from Bio import SeqIO
from Bio.Restriction import RestrictionBatch, EcoRI, BamHI

batch = RestrictionBatch([EcoRI, BamHI])

for record in SeqIO.parse('sequences.fasta', 'fasta'):
    analysis = Analysis(batch, record.seq)
    results = analysis.full()
    print(f'{record.id}:')
    for enzyme, sites in results.items():
        if sites:
            print(f'  {enzyme}: {sites}')
```

## Notes

- **Positions are 1-based** - first base is position 1
- **Cut position** - where enzyme cuts (between bases)
- **Linear default** - set `linear=False` for circular DNA
- **Case insensitive** - recognition matches regardless of case
- **Ambiguous bases** - some enzymes recognize N, R, Y, etc.

## Related Skills

- restriction-mapping - Visualize cut positions on sequence
- enzyme-selection - Choose enzymes by criteria
- fragment-analysis - Analyze resulting fragments