Universal promoter for gene expression without cloning: expression-PCR.

We present a rapid and simple system called expression-PCR (E-PCR) for in vitro synthesis of functional protein from genomic or plasmid DNA. A universal promoter was developed containing an untranslated leader sequence from alfalfa mosaic virus directly downstream from the T7 bacteriophage promoter. When this universal promoter is spliced to a DNA segment, it produces a suitable template for in vitro transcription and translation. The DNA to be expressed is first amplified by the PCR using a 5'-primer that incorporates an area homologous to the 3'-end of the universal promoter. The universal promoter and this DNA fragment are mixed and re-amplified in a reaction analogous to splicing by overlap extension, generating a recombinant DNA template that can be transcribed and translated in vitro without further processing. Unlike standard methods for in vitro transcription and translation, E-PCR is not dependent upon specialized transcription vectors, cloning, plasmid isolation and purification, or restriction enzyme sites. This approach has been used to synthesize and examine the biological activity of malaria proteins that are vaccine candidates for Plasmodium falciparum. E-PCR represents a significant improvement over current in vitro expression systems, most notably in its time savings, versatility of gene expression and its compatibility with rapid PCR-based site-directed mutagenesis procedures.