Ribozyme cleavage is efficient in vivo. Total RNA was isolated from strains expressing lacZ-HH+ mRNA (lane 1), lacZ-HH− mRNA (lane 2), or wild-type lacZ mRNA (lane 3) and was subjected to primer extension analysis. DNA sequencing of pMC55 (lacZ-HH−) was performed, and reactions were run in adjacent lanes (G, C, T, and A). A portion of the cDNA complementary to the hammerhead sequence is shown, with the cleavage site indicated by the arrow. This experiment was performed twice with virtually identical results.