Inhibition of gene expression by a short sense fragment

In order to further investigate the mechanism of antisense inhibition of gene expression, a series of plasmids which generate short antisense RNAs deriving from the 5' end of the CAT gene were constructed. When transfected into COS1 cells, these constructions were capable of specifically reducing CAT gene expression. Unexpectedly, transfection with constructions expressing defective RNA in the sense orientation also resulted in reduced levels of both CAT enzyme and mRNA. This was mediated by both short and full-length CAT-gene fragments, and was dependent on the presence of the tested transcriptional promoters, either the herpes simplex virus thymidine kinase (TK) or simian virus 40 late (SVL) promoters. These results, in conjunction with computer aided secondary structure prediction, indicate a possible similarity of regulatory mechanism for both senses of RNA acting within the cell.