[Design and preparation of the multimeric self-cleavable hammerhead ribozyme targeting apple scar skid viroid and its activity detection in vitro].

A self-cleaving hammerhead ribozyme gene containing a 14nt target sequence of ASSVd at the 3' end of hammerhead ribozyme was synthesized, amplified and cloned at the Xho I-Hind III site of pGEM7Zf(+). The ends produced by Xho I or Sal I can link together, thus the recognition sites of both enzymes vanish and can't be cut by either one. We used this property to get the recombinant plasmid bearing 2, 4, 6, 8, 10 and 12 copies of self-cleavable ribozyme respectively after successively sub-cloning five times. Linearized recombinat plasmid model catalyzed by T7 RNA polymerase was transcribed in vitro. The multimeric ribozyme molecules efficiently self-cleaved via cis-acting to release many ribozyme molecules It indicates that the concentration of ribozyme transcripts has been enhanced during transcription. Trans-cleavage reaction was carried out by incubating monomeric and multimeric ribozymes with same mol concentration and 32P labeled target ASSVd. Both ribozymes and target transcripts were mixed in 1:1 ratio. Autoradiograms showed the transcripts of multimeric ribozyme were substantially more effective against the ASSVd target RNA than the monomeric ribozymes. We confer that the multimeric self-clevable ribozyme is likely to provide more valuable application in vivo.