General plasmids for producing RNA in vitro transcripts with homogeneous ends.

In vitro transcripts of bacteriophage RNA polymerases (RNAPs), such as T7 RNAP, often suffer from a considerable degree of 3'-end heterogeneity and, with certain promoter sequences, 5'-end heterogeneity. For some applications, this transcript heterogeneity poses a significant problem. A potential solution is to incorporate ribozymes into the transcripts at the 5'- and/or 3'-end of the target RNA sequence. This approach has been used quite widely but has required the generation of new transcription vectors or PCR-derived templates for each new RNA to be studied. To overcome this limitation, we have created two general plasmids for producing homogeneous RNA transcripts: one encodes a 3'- hepatitis delta virus (HDV) ribozyme and the other, used in combination with a two-step PCR, allows the production of double [5'-hammerhead (HH) and 3'-HDV] ribozyme constructs. A choice of cloning and run-off transcription linearisation restriction enzyme sites ensures that virtually any RNA sequence can be cloned and transcribed from these plasmids. For all the RNA sequences tested, good yields of transcript were obtained. These plasmids provide the tools for the simple, rapid creation of new RNA-coding plasmids to produce milligram quantities of homogeneous in vitro transcripts for all applications.