Nucleotide sequence and proposed secondary structure of designed variants of HDV antigenome ribozyme. (a) The wild type HDV antigenome ribozyme. (b)-(e) Variants of antigenome ribozyme: SBL (b), LSB (c), and the families LBS (d) and BLS (e). Inserts show the spacer sequence and activity (k1, min-1). The nucleotides are numbered according to Rosenstein and Been . P2–P4, stems 2–4; P1.1, stem 1.1; s1, substrate containing part of stem P1; R, substrate recognition part of stem P1; J1/2, J1/4, J4/2, nucleotide sequences connecting stems P1 and P2, P1 and P4, P4 and P2; l2, l3 and l4, sequence connecting 5' and 3' sides of P2, P3 and P4; Sp (spacer), sequence connecting two ribozyme parts (L and S or B and S); f (forepart), an oligonucleotide which is always located at the 5'side of S chain. Only SBL topology corresponds to natural ribozyme.