Naturally occurring antisense RNA control--a brief review.

Biological control by naturally occurring anti-sense RNAs has been documented in a number of prokaryotic cases, and strongly suggested in several eukaryotic systems. The biological activities controlled are diverse, including transposition, phage development, chromosomal gene expression, and plasmid replication, compatibility and conjugation. Control is exerted at many different levels, by both direct and long-range effects. The stem/loop structures common to all anti-sense RNAs are important functional domains: loops are the sites of critical interactions in the initiation of pairing to the target RNA; stems determine anti-sense RNA stability in vivo. These features need to be considered in the design of artificial anti-sense RNA control. Details of RNA/RNA pairing have emerged; pairing initiates at single-stranded regions in anti-sense RNA loops, and stable complex formation involves the nearby end of one or both molecules.