A Tetracycline-Regulated Expression System without Viral Transactivators
The T-REx™ System yields higher levels of induced expression than any other regulated mammalian expression system. It utilizes the complete CMV promoter and adds control elements from the bacterial tetracycline resistance operon to effectively repress and derepress transcription from one of the strongest mammalian promoter sequences known (1,2).

Specific Activation
The T-REx™ System uses a repressor mechanism that blocks transcription from the powerful CMV promoter in the absence of tetracycline. Because the T-REx™ System elements do not use viral transactivators, you can achieve high-level expression from the complete CMV promoter without secondary, non-specific activation of host genes.

The T-REx™ Mechanism
The T-REx™ transcriptional control elements are illustrated in Figure 1. Two tetracycline operator sequences (TetO₂) have been inserted between the TATA box of the CMV promoter and the transcriptional start site. The TetO< sub>2 sequence itself has no effect on expression. When the tetracycline repressor protein (TR) is present, it effectively binds the TetO₂ sites and blocks transcription initiation. Tetracycline added to the culture medium binds to, and changes the conformation of, the TR protein. This change causes the TR protein to release the TetO₂ sites, derepressing transcription from the CMV promoter. The result is high-level expression of the gene of interest (Figure 2). Expression levels can be modulated based on the tetracycline concentration and can be induced to levels that are achieved with constitutive CMV expression vectors.
T-REx™ is a powerful inducible mammalian expression system that allows you to regulate expression from the complete human cytomegalovirus (CMV) enhancer-promoter. T-REx™inducible expression vectors offer the following features:

• Complete CMV enhancer-promoter sequence containing two copies of the tetracycline operator TetO₂ sequence for high-level regulated expression
• Zeocin™ or hygromycin resistance gene for effective selection of stable mammalian cell lines
• Large multiple cloning site to simplify cloning

In addition , pcDNA™4/TO/myc-His offers a c-myc epitope for rapid detection of the recombinant protein with an Anti-myc Antibody and a polyhistidine (6xHis) sequence for simple purification of the recombinant protein with nickel-chelating resin and detection with Anti- His(C-term) Antibody.

The regulatory vector, pcDNA™6/TR, is provided for high-level expression of the tetracycline repressor (TR) protein. This vector expresses the Blasticidin resistance gene for rapid selection of mammalian cell lines that stably express the TR protein.