In Vitro Transcription Vector (for mRNA)
Overview

Our in vitro transcription vectors are simple and efficient systems for RNA synthesis, applicable for a variety of research purposes. The mRNA version of the in vitro transcription vector system is ideally suited for producing mRNAs for in vitro translation, biochemical studies, protein expression after injection into cells or embryos, and other applications requiring mRNAs of defined sequences.

This system utilizes a T7 promoter upstream of your sequence of interest, facilitating highly efficient production of mRNA by T7 bacteriophage RNA polymerase (T7 RNAP) under appropriate reaction conditions and in the presence of nucleotide triphosphates. We recommend that you follow established in vitro transcription protocols available in published literature.

T7 RNAP has certain base requirements for efficient transcription initiation which have been already incorporated into the vector design. The first two nucleotides of the transcribed mRNA will be GG, corresponding to the 3’-end of the T7 promoter sequence, followed by your transcript sequence of interest.

Our in vitro transcription vector for mRNA synthesis is engineered for run-off transcription. This means that the T7 RNAP proceeds to the end of the DNA template during transcription, and does not terminate at any specific site within the plasmid. For this reason, the circular plasmid template should be linearized by restriction digestion with SapI, BsiWI, or AscI prior to in vitro transcription for ensuring the length and sequence of the generated transcripts. Any of these enzymes will cut the plasmid at unique sites immediately downstream of the poly(A) sequence. Care should be taken that the sequence to be transcribed does not contain any restriction sites for the linearization enzyme used, as this would result in unstable, truncated mRNA transcripts. Contaminants from the digestion reaction may inhibit the subsequent T7 RNAP transcription reaction, therefore purification via column or phenol:chloroform extraction following digestion is recommended. However, it is generally not necessary to purify the promoter and insert fragment away from other fragments, because only the fragment containing the T7 promoter sequence will serve as a template for transcription.

In vivo, the addition of a 7-methylguanosine cap to the 5' end of mRNA transcripts is essential for RNA stability, efficient translation, nuclear transport, and splicing. Likewise, for majority of research applications of in vitro transcribed mRNA, capped RNA is desired. RNA capping of your transcripts can be carried out either co-transcriptionally, using cap analogs, or post-transcriptionally, using capping enzymes. Both methods produce functional, capped RNA suitable for injection, in vitro translation, and other applications.

For further information about this vector system, please refer to the papers below.

References Topic
Nucleic Acids Res. 7:1931 (1979) Cloning and characterization of the T7 promoter
Methods Mol Biol. 703:29 (2011) Protocols for the synthesis of RNA by in vitro transcription
J Vis Exp. 61:3702 (2012) ping, and transfection of mRNA
Protein Expr Purif. 9:142 (1997) Protocol for expression and purification of T7 RNAP for in vitro transcription
Highlights

Our in vitro transcription vectors for mRNA synthesis are designed to serve as highly effective templates for T7 RNAP-mediated in vitro transcription. This vector system is optimized for high copy number replication in E. coli, efficient restriction digestion, and abundant mRNA production.

Advantages

High efficiency: T7 RNAP is a robust and highly efficient enzyme. T7 RNAP-dependent in vitro transcription reactions can produce large amounts of functional RNA.

Technical simplicity: In vitro transcription using a plasmid template and T7 RNAP is technically straightforward, and far easier than mRNA expression in cells, which requires transfection and cell culture.

Disadvantages

Specified orientation: This vector system contains a single promoter for in vitro transcription. The orientation of the sequence of interest relative to the T7 promoter will determine the sequence transcribed. If both sense and anti-sense transcripts are desired, two vectors will be needed.

Run-off transcription: Efficient in vitro transcription using this vector system requires linearization of the plasmid by restriction digestion prior to the transcription reaction.

Key components

T7 promoter: A promoter for the RNA polymerase from T7 bacteriophage. Drives high-level transcription of the downstream sequence of interest.

Transcribed sequence: Your DNA sequence of interest to be transcribed into RNA is placed here.

poly(A): Thirty base poly(A) track. Adds stability to the transcribed mRNA.

SapI, BsiWI, AscI: Unique restriction endonuclease sites that can be used to linearize the plasmid prior to in vitro transcription.

pUC ori: pUC origin of replication. Plasmids carrying this origin exist in high copy numbers in E. coli.

Ampicillin: Ampicillin resistance gene. It allows the plasmid to be maintained by ampicillin selection in E. coli.