gBlocks Gene Fragments

Double-stranded, linear, nucleic acids with the perfect combination of excellent sequence fidelity, affordability, and application flexibility

gBlocks Gene Fragments are sequence-verified, double-stranded DNA fragments that ship in only a few working days for affordable and easy gene construction or modification, applications such as antibody research and CRISPR-mediated genome editing, use as qPCR standards, and more. gBlocks Gene Fragments are available in tubes or plates.

  • Start your projects quickly with shipping in as few as 2 business days
  • Secure discounts for large-volume orders


Individual fragments in tubes

A, T, C, and G residues only. Delivered dry and normalized to 250, 500, or 1000 ng, depending on length.

Fragment libraries in tubes

Available in lengths of 251–500 bp. Up to 18 consecutive N or K residues. Delivered dry, normalized to 200 ng.

Fragments in plates

Available for fragments of 125–3000 bp. Orders require a minimum of 36 fragments per plate. Resuspended in 25 μL of nuclease-free water (concentration: 10 ng/μL). Shipped on dry ice and delivered within 10 business days of order confirmation (excluding Fridays). See below for pricing, per fragment, based on fragment length. Libraries not available in plate format.


1 BD: business days. Shipping time is dependent on length and complexity of the gBlocks fragments ordered. In a few cases, shipping time may exceed the estimated time.

Sequence Information is secure and confidential at IDT. Please see our Confidentiality Statement for more information.

gBlocks Gene Fragments are sequence-verified, double-stranded DNA molecules 125–3000 bp in length. They are manufactured with the same industry-leading, high-fidelity synthesis chemistries that were developed for our Ultramer DNA Oligos. Their outstanding quality and rapid delivery time make them ideal for quick gene construction or modification, and any other application requiring double-stranded DNA. These include, but are not limited to:

  • CRISPR-based genome editing
  • Recombinant antibody engineering
  • qPCR and PCR controls
  • Enzyme engineering
  • Vaccine research
  • High resolution melt (HRM) assays

gBlocks Gene Fragments in plates

For projects that require large quantities of gBlocks Gene Fragments (≥36 fragments at a time), delivery in plates may be a more cost-effective option.

gBlocks Gene Fragment Libraries

gBlocks Gene Fragment Libraries are pooled gBlocks fragments that are ideal for demanding applications, such as generating recombinant antibodies or protein engineering. While gBlocks fragments can be used directly in applications, such as in vitro transcription, or as standard or internal controls for qPCR or NGS experiments, they are most often assembled into functional genes or longer constructs by seamless assembly techniques or traditional restriction cloning. With gBlocks Gene Fragments Libraries, you can generate hundreds of thousands of constructs at a fraction of the cost that creating multiple variant libraries would require.

Ordering gBlocks libraries is just as easy as ordering standard gBlocks Gene Fragments. The tool’s interface allows N or K (G or T) mixed bases; however, they must be entered in the appropriate format. gBlocks Gene Fragments in the libraries can be 251 to 500 bp in total length, including the variable region. The variable regions can be up to 18 consecutive N or K bases long, and must be at least 125 bp from either end of the gene fragment (Figure 1).

Figure 1. Ordering format for gBlocks Gene Fragment Libraries. Placing a K mixed base in the third position of codons eliminates the TAA and TGA stop codons from being included in the gene fragments libraries, leaving only TAG as the possible stop codon.

Need something else? Tell us about it! We realize that we have a limited offering for gBlocks Gene Fragments Libraries. We will be offering more complex libraries in the future. Help us prioritize our product development by sharing what you need from us with as much detail as possible (i.e., show us sequences, including features such as mixed bases, annotations, and drawings) and send to libraries@idtdna.com.

Why do we limit the variable regions to 18 mixed bases?

When you order a gene fragment library that contains 18 "N" mixed bases, you order a pool of 418 gene fragments—about 68.7 billion different gBlocks Gene Fragments. Increasing the number of variable bases beyond 18 would result in more sequence combinations than can be accommodated in the 200 ng of product provided, which would compromise the overall representation of sequences within the pool.

Robust and flexible assembly

gBlocks Gene Fragments can be easily assembled and cloned into the vector of your choice using a variety of cloning methods, including the Gibson Assembly® method [1] and blunt- or cohesive-end cloning protocols. The fidelity of gBlocks fragments substantially reduces the number of clones that need to be sequenced to identify the intended construct when compared to other methods of gene assembly using DNA oligonucleotides. Note that assembly methods such as blunt-end cloning and restriction cloning consistently demonstrate lower fidelity. For added flexibility, you can order gBlocks Gene Fragments with or without a 5′-phosphate group

Adding diversity at reasonable cost

For screening purposes, gBlocks Gene Fragments Libraries allow for the generation of hundreds of thousands of constructs at a fraction of the cost of generating variant libraries.


  1. Gibson D, Young L, et al. (2009) Enzymatic assembly of DNA molecules up to several hundred kilobases. Nat Methods, 6(5):343–345.

Quality assurance

Every gBlocks Gene Fragment you receive goes through the following verification process:

  1. Sequences (125–3000 base pairs) are entered on the gBlocks Gene Fragments order entry page. A, C, G, T bases, as well as up to 18 consecutive N or K variable bases can be entered. Other mixed degenerate bases are currently not available, and neither are “modified" bases (inosine, uridine).
  2. Upon order entry, the entered sequences are reviewed by both our automated screening tools and our scientists to identify characteristics that may interfere with synthesis.
  3. Biosafety and regulatory conformance check:
    • A biohazard disclosure statement is required for each gene order.
    • IDT reserves the right to refuse any order that does not pass this analysis. If one of your sequences does not pass the screen criteria, you will be contacted by a gene services specialist to determine the best way to proceed.

Quality control and sequence verification

Each gBlocks Gene Fragment undergoes the following quality control procedures:

  1. Size verification by capillary electrophoresis
  2. Sequence identification by mass spectrometry

This rigorous testing ensures that, in the majority of cases, >80% of recombinant colonies obtained from cloning each gBlocks Gene Fragment will contain the desired insert. More complex sequences may suffer from reduced fidelity, which can be addressed by the end user sequencing additional clones.

For gBlocks Gene Fragment Libraries, each constant region is verified as above. The final library product is size verified by capillary electrophoresis.

High fidelity gene fragments simplify the cloning process

gBlocks Gene Fragments possess the high sequence fidelity and DNA purity (Figure 1) necessary for synthetic biology and gene assembly methods.

Figure 1. gBlocks Gene Fragments facilitate accurate production of synthetic genes. Sequencing of 262 gBlocks Gene Fragments demonstrates consistent quality of gBlocks across various lengths. The gBlocks fragments prepared for sequencing using a Nextera® kit (Illumina). Purity was determined by counting the observed errors in the assembled sequences and subtracting the background of error rate of the machine.

Compatibility with traditional cloning methods and vectors

gBlocks Gene Fragments are compatible with all cloning methods that require double-stranded DNA as a starting material, allowing easy assembly of your desired construct sequence into your favorite cloning system.

Table 1. gBlocks Gene Fragments are compatible for cloning in a variety of standard vectors, using common cloning methods.*

Cloning methodNo. of correct clonesNo. of clones sequencedWild-type clones (%)
Restriction cloning273284
TOPO® cloning3475

* Single gBlocks Gene Fragments ranging between 223 and 296 bp were cloned into pUC57, pBluescript II, pET27, psiCHECK-2, Zero Blunt TOPO, pIDTSMART, and pGEM T Easy plasmids. Resulting clones were sequence verified by double-stranded sequencing.

Sequence Information is secure and confidential at IDT. Please see our Confidentiality Statement for more information. All online ordering steps, including sequence entry and your choice of parameters, are also secure and protected.

We screen the sequence of every gene fragment order we receive to (1) identify any regulated and other potentially dangerous pathogen sequences, and (2) verify that IDT’s gene customers are legitimate scientists engaged in beneficial research.

IDT is among the five founding members of the International Gene Synthesis Consortium (IGSC) and helped to create the IGSC’s Harmonized Screening Protocol. The Harmonized Screening Protocol describes the gene sequence and customer screening practices that IGSC member companies employ to prevent the misuse of synthetic genes. IDT takes the steps set out in the Harmonized Screening Protocol to screen the sequences of ordered genes and the prospective customers who submit those orders.

For more information about the IGSC and the Harmonized Screening Protocol, please visit the website at www.genesynthesisconsortium.org.


In October 2010, the United States government issued final Screening Framework Guidance for Providers of Synthetic Double-Stranded DNA, describing how commercial providers of synthetic genes should perform gene sequence and customer screening. IDT and the other IGSC member companies supported the adoption of the Screening Framework Guidance, and IDT follows that Guidance in its application of the Harmonized Screening Protocol. For more information, please see 75 FR 62820 (Oct. 13, 2010), or https://federalregister.gov/a/2010-25728.

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