Twist Bioscience Variant Libraries | Site Saturation Variant Libraries

Twist Bioscience Variant Libraries | Site Saturation Variant Libraries

Generate 99% of Desired Variants

Protein engineering screens using single site variant libraries allow researchers to explore a protein’s sequence space and investigate the relationship between sequence and protein structure and function.

Twist Site Saturation Variant Library construction leverages massively parallel oligonucleotide synthesis using Twist's proprietary silicon-based DNA synthesis platform. Twist libraries are NGS-verified to confirm that all desired variants are present in the correct ratios.

Precisely Crafted Variant Libraries
  • Complete control over codon usage (all 64 codons available)
  • High uniformity of variant representation at every site
  • No unwanted codons or premature stop codons

Verified Quality
  • Rigorous quality control
  • Verified uniformity of variant representation by NGS
  • Representation of each site normalized by mass

  • One position per well in a 96 well plate or all positions pooled in a single tube
  • Screen 1 to 20 different amino acids at each position



Experience base by base precision

Learn more about how Twist Single Site Variant Libraries (SSVL) enable the interrogation of sequence space to identify key residues in protein structure and function.

Precision Synthesis of Variant Libraries Enables Comprehensive Interrogation of Single-Site



Explore the Sequence Space

Site Saturation Libraries eliminate codon bias and unwanted substitutions unlike traditional methods such as degenerate and NNK approaches. 

TRIM offers a poor repetitive yield, leading to <50% full-length product in a typical library whereas, Twist libraries yield more usable variants, increasing effective library size.



Eliminates sequence bias No No Yes
Number of codons available Unknown 32 All 64
Prevents undesirable motifs No No Yes
Allows codon optimization No No Yes
Avoids stop codons No Yes Yes


Highly Uniform Variant Libraries

Site Saturation Variant Libraries enable efficient sampling of a protein’s sequence space in screening assays.

This figure shows the observed distribution of amino acids across  65 positions in protein (19 intended variants per position) when built with Twist SSVLs versus error prone PCR. The bars represent a different amino acid position, with each color indicating the observed variant frequency. All variants are present in the expected ratios in the Twist Library.

SSVL Distribution


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