Cytotoxic hammerhead ribozymes

Small catalytic RNA molecules of the hammerhead ribozyme type were found to have cytotoxic effects unrelated to their intended activity, An expression library of ribozyme sequence variants was constructed in a recA-deficient strain of Escherichia coli such that individual library members differed in regions designed to form base pairs with human immunodeficiency virus-1 (H IV-1) tat mRNA, The parental ribozyme and many variants exhibited a bacteri ostatic effect. One variant studied in detail was also bactericidal. When i ts expression was induced, ribozyme-dependent inhibition of bacterial growt h was not observed in recA(+) or recA(+) lexA3 (Ind(-)) cells, suggesting t hat the recombination function of the RecA protein, not the absence of the SOS response, is sufficient to alleviate the cytotoxic effect. These data d ocument the need for careful testing for toxic effects during intracellular studies of ribozyme action.