Hammerhead ribozymes and stable stem loop structures function as inhib
itors of 3'-5'-exonuclease degradation of external guide sequences (EG
Ss) when covalently linked to the 3'-end of EGS RNAs. This observation
may be of use in improving the efficiency of gene inactivation techni
ques that use single-stranded RNA (e.g., antisense RNA, EGS RNA) in vi
vo.