Plant 7SL RNA and tRNA(Tyr) genes with inserted antisense sequences are efficiently expressed in an in vitro transcription system from Nicotiana tabacum cells.

RNA polymerase III-driven cassettes for the expression of antisense RNAs and ribozymes have recently attracted much attention because (1) pol III genes are transcribed abundantly in all kinds of tissues and (2) the transcripts are very stable by virtue of their small and compact size. We have designed two types of pol III-based expression vehicles. Antisense RNA sequences targeted against conserved structural elements or domains in the RNAs of potato spindle tuber viroid, hop latent viroid and potato virus S were either embedded in the anticodon region of a Nicotiana tRNA(Tyr) gene or near the 3' end of an Arabidopsis 7SL RNA gene. Both classes of chimeric genes were transcribed in vitro in a homologous plant extract. Our studies clearly revealed that the modified tRNA and 7SL RNA genes, carrying insertions of up to 90 and 120 bp, respectively, were expressed efficiently in the tobacco nuclear extract, resulting in high levels of stable chimeric transcripts. 7SL RNA (also termed SRP RNA) represents the RNA component of the signal recognition particle. This is the first report of demonstrating the employment of 7SL RNA genes as potential cassettes for the expression of antisense RNA and ribozyme sequences and might be helpful in future experiments to control their localization in specific sub-cellular compartments.