Production of circular streptavidin RNA aptamer in vivo.

RNA aptamers is one of highly hopeful candidates for RNA therapeutics. We previously reported an in vitro production of a circular streptavidin RNA aptamer. Here we show an application for producing the circular RNA aptamer in vivo. First, we constructed a circular RNA expression vector that contained self-splicing permuted intron-exon (PIE) sequences between T7 promoter and T7 terminator sequences so as to be transcribed by T7 RNA polymerase produced in JM109(DE3) cells. RNA expression driven by T7 RNA polymerase was triggered by addition of IPTG and the circularized RNA was generated from the resulting PIE transcripts. Circular streptavidin RNA aptamer generated in the JM109(DE3) cells was detected by a two dimensional denaturing PAGE analysis using the ethidium bromide staining. Northern blot analysis using a self-ligated sequence specific oligo DNA probe and sequencing analysis revealed that the self-splicing and circularization process precisely occurred in E. coli. The circular aptamer was easily purified by a solid phase DNA probe method from a partially purified total RNA fraction. This is the first demonstration of an in vivo expression of a circular RNA aptamer and its purification, paving the new way for inexpensive production of RNA aptamer.