Activation of HIV-specific ribozyme activity by self-cleavage

A hammerhead ribozyme designed to cleave in trans the R region of HIV-1 RNA was inserted into a eukaryotic expression vector. This ribozyme was studied in vitro using the T3 RNA polymerase promoter located upstream of the eukaryotic promoter. The ribozyme showed no activity against its specific target sequence under any condition tested. To decrease the influence of potential cis inhibitory sequences in such a ribozyme transcript, a specific target sequence was inserted upstream of the ribozyme-coding sequence. This insertion allowed the release by cis cleavage of a short RNA bearing ribozyme activity and able to cleave in trans an external RNA target. The cis cleavage reaction generated two RNA molecules: the shorter RNA species, which included the catalytic domain, showed a trans cleavage reaction. This self-cleavable ribozyme was active in vitro at 37 degrees C against three distinct HIV-1 transcripts sharing the specific target sequence. Ribozyme activity was thus attained by self-cleavage of the ribozyme-containing sequence from the longer vector transcript.