Mechanism of action of antisense RNA. Sometime inhibition of transcription, processing, transport, or translation.

Anyone considering the use of AS RNA, generated endogenously, to inhibit gene expression should plan to generate several independent transfectants with nonoverlapping sequences; strategies that maximize both the transcription rate and the stability of the AS RNA are obviously desirable. Reasons why different results are obtained in different systems or with different constructs likely include the specific nucleotide sequence under investigation, the location of the AS gene in the nucleus relative to the endogenous gene, and the rate-limiting step in the expression of the target gene. Splicing may not be necessary, but an efficient polyadenylation signal likely is. Employment of a ribozyme-mediated strategy, discussed by various investigators in this volume, may be beneficial. There is no reason at present to conclude that any gene, however abundant its transcript might be, is inherently recalcitrant to AS-mediated down-regulation of expression.