Artificial immune system against viral infection involving antisense RNA targeted to the 5'-terminal noncoding region of coliphage SP RNA

We previously reported the utilization of antisense RNA in the development of a novel immune system against RNA coliphage SP proliferation (Hirashima et al. [1986] Proc. Natl. Acad. Sci. U.S. 83, 7726-7730). We attempted to determine the most effective (i.e., those eliciting antiviral activity) sequences for targeting micRNAs within the 5'-terminal noncoding region of 54 nucleotides (nt). It was found that a 30-nt micRNA against the sequence from base 32 to 61 exhibited nearly complete inhibition of phage production. Upon further dissection of this sequence, it was concluded that the most effective micRNA against phage SP production should contain the sequences complementary to the Shine-Dalgarno (SD) sequence of the first gene and its 13-nt upstream sequence. The addition of downstream sequences had little effect. These results suggest that the micRNA functions by preventing the binding of ribosomes to the SD sequence of the first gene. The addition of further upstream sequences had a significant negative effect on the micRNA function, indicating that the removal of such impeditive sequences from a micRNA is an important strategy for the development of a potent micRNA immune system.