FIG. 1.

Ribozyme-based gene inactivation strategy and δRz secondary structure. (A) The ribozyme binds specifically to an accessible single-stranded region of the target mRNA through a series of Watson-Crick base pairs. Some mRNA target sites are less accessible to the ribozyme depending on their secondary and tertiary structures. Moreover, the association of proteins (solid ovals) with the mRNA in vivo may also prevent ribozyme binding to potential target sites. After binding, the second step consists of specific cleavage of the target mRNA by the ribozyme. Following cleavage, the mRNA is rapidly degraded by the host nucleases (“PacMan” symbols). (B) Secondary structure of the trans-acting antigenomic δRz bound to its substrate or target. The stems are designated P1 to P4. The P1.1 pseudoknot is indicated by dotted lines. The homopurine base pair (G • • G) at the top of the P4 stem and the wobble base pair (G • U) in the substrate recognition stem (P1) are also indicated. The arrow indicates the substrate cleavage site. H at position −1, in reference to the cleavage site, indicates nucleotide A, C or U, while N indicates any nucleotide (A, C, U, or G).