A sequence-specific ribozyme (M1GS RNA) derived from the catalytic RNA subunit of RNase P from Escherichia coli was used to target the mRNA encoding the major transcription regulatory protein Rta of Kaposis sarcoma (KS)-associated herpesvirus (KSHV).A reduction of more than 90％ in the expression level of RTA mRNA and a reduction of about 250-fold in viral growth were observed in human cells that expressed the ribozyme.