We work hard for our customers. Our various research groups are trying to find better, quicker and easier ways to purify DNA manually or using automation, to assay cell viability or apoptosis and yes, even to clone and express your protein of interest. Our Flexi^® Cloning System is a simple and powerful method of directional cloning with a wide array of vectors suitable for many downstream uses, including adding protein expression tags, studying mammalian protein interactions, performing in vitro expression and expressing fusion proteins.

However, as useful as the Flexi^® Vectors may be, the nomenclature may be confusing. For example, what is the difference between pFN6A (HQ) Flexi^® Vector and pFC7K (HQ) Flexi^® Vector? Let us decipher the terminology used.

The lower case p designates that the product is a plasmid.

The letter F indicates the plasmid is in the Flexi^® Vector family.

The letters N and C (if present) refer to the location of a fusion tag or a reporter coding region. That is, is it N-terminal or C-terminal? This is important to know as the location of a fusion tag or coding region can affect expression of the protein cloned into the vector.

The number (6 or 7 in this example) means these vectors were the sixth and seventh vectors created in the Flexi^® Vector family. This will not affect you much but helps to distinguish which vector you are using.

The letter A or K refers to the E. coli antibiotic resistance present on the plasmid. The A vectors carry ampicillin resistance, while the K vectors are resistant to kanamycin. The antibiotic resistance is important to know for the Flexi^® Vector cloning strategy (discussed here).

The items in parentheses, HQ in this example, refer to the tag or coding region carried on the vector. HQ stands for histidine-glutamine, a metal-affinity tag present on the vector. The N and C designations mentioned earlier indicate the position of the tag relative to the protein-coding region encoded by the insert.

Any items following the parentheses (e.g., CMV or T7) refer to the promoter that drives protein expression.

Therefore, the pFN19K (HaloTag^® 7) T7 SP6 Flexi^® Vector creates an N-terminal fusion of a cloned protein and the HaloTag^® 7 coding region, which can be expressed from the T7 or SP6 promoter. The plasmid can be grown and propagated in E. coli using kanamycin selection.

Now that the terminology is clear, how do you choose a Flexi^® Vector for your experiment? That will be discussed my next entry. Stay tuned!

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Sara Klink

Technical Writer at Promega Corporation

Sara is a native Wisconsinite who grew up on a fifth-generation dairy farm and decided she wanted to be a scientist at age 12. She was educated at the University of Wisconsin—Parkside, where she earned a B.S. in Biology and a Master’s degree in Molecular Biology before earning her second Master’s degree in Oncology at the University of Wisconsin—Madison. She has worked for Promega Corporation for more than 15 years, first as a Technical Services Scientist, currently as a Technical Writer. Sara enjoys talking about her flock of entertaining chickens and tries not to be too ambitious when planning her spring garden.

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