Antisense RNA: its functions and applications in gene regulation--a review.

All known antisense RNAs existing in nature are described. Of 11 natural antisense RNAs, nine function at the level of transcription and two at the level of DNA replication. On the basis of their inhibitory mechanisms they can be separated into three classes. From what can be found in the naturally occurring antisense RNAs, strategies in designing artificial antisense RNAs for gene expression are proposed, and applications and potential problems discussed.