Are there any molecular biology knowledge sites that focus on sequence design choices and synthesis constraints?

Yes — there are a few useful resources, though most sequence-design and synthesis-constraint guidance is spread across vendor docs, standards pages, and specialized tools rather than a single “knowledge site.”

Here are some good places to look:

1. IDT Knowledge Resources

• Integrated DNA Technologies (IDT) has extensive technical pages on oligo, gRNA, gene fragment, and qPCR design.
• Good for:
  • GC-content guidance
  • Secondary structure avoidance
  • Repeats/homopolymers
  • Synthesis length limits
  • Modifications and purification options
• Start with their design and application notes.

2. Thermo Fisher / Invitrogen design guides

• Useful for:
  • PCR primer design
  • cloning constructs
  • synthetic gene constraints
  • codon optimization basics
• Often more application-oriented than theory-heavy.

3. Twist Bioscience knowledge base / design guidelines

• Especially strong for:
  • synthetic gene design
  • sequence complexity constraints
  • assembly-friendly design
  • avoid problematic repeats and extreme GC
• Good if you care about synthesis and library construction.

4. Genscript resources

• Has practical guides on:
  • gene synthesis
  • codon optimization
  • vector/cloning design
  • sequence constraint handling
• Useful for understanding what vendors will or won’t synthesize.

5. Benchling learning center / docs

• More tool-focused, but useful for:
  • sequence annotation
  • primer/construct design workflows
  • plasmid and assembly planning
• Less about hard synthesis constraints, more about design process.

6. NCBI / Primer-BLAST and related docs

• Best for primer design and specificity considerations.
• Helpful if you want sequence design with constraints like off-target avoidance.

7. Addgene educational resources

• Good conceptual explanations for:
  • cloning strategy
  • vector design
  • regulatory element choices
  • construct assembly considerations

8. Standards and community resources

• SBOL (Synthetic Biology Open Language): useful for design standards and sequence-level representation.
• iGEM wiki and resources: practical, community-driven synthetic biology design guidance.

9. Tool/documentation sites for constraint-aware design

If you want design choices directly tied to synthesis limits, these are especially relevant:

• Primer3 docs
• Benchling guides
• Geneious documentation
• DNA Chisel documentation (for optimizing sequences under constraints)
• Cassette and assembly design tools from academic groups

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What to look for in a good site

A site focused on sequence design and synthesis constraints should ideally cover:

• GC extremes
• repeats / low complexity
• hairpins and dimers
• homopolymers
• methylation-sensitive motifs
• restriction site constraints
• assembly compatibility
• oligo vs gene-fragment vs plasmid synthesis limits
• codon optimization / deoptimization
• sequence screening for problematic motifs

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If you want one “best starting point”

For practical synthesis-aware design, I’d start with:

1. IDT design guides
2. Twist Bioscience guidelines
3. DNA Chisel for constraint-aware optimization
4. Benchling for workflow/design integration

If you want, I can also give you:

• a curated list of exact links
• sites specifically for gene synthesis constraints
• or sites focused on oligo/primer design vs full-gene design