RESUMEN
We conducted extensive mutagenesis analysis on a hepatitis delta virus (HDV) genomic ribozyme to study the sequence specificity of certain region and to derive the secondary structure associated with the catalytic core. The results confirmed that the autocatalytic domain of HDV genomic RNA contained four base-pairing regions as predicted in the 'pseudo-knot' model [Perrotta & Been (1990) Nature 350, 434-436]. The size and sequence of one of the base-pairing regions, i. e. stem-and-loop, could be flexible. Helix 3 and the first basepair of helix 1 required specific sequence to retain self-cleavage activity. The structural requirement of helix 2 was less stringent than the other base-pairing regions. Moreover, the size of helix 1 affected self-cleavage whereas the length of hinge could be variable even though the first three residues of hinge had stringent sequence requirement.
