Abstract: The present invention provides a simple, specific and nontoxic gene knock-out method by formation of covalently bonding between modified probes and targeted sequences. When covalently modified first strand probes are hybridized with a second strand of targeted gene transcripts, certain modified bases of said first strand will interact with natural bases of said second strand to form covalent bonds by which the translation of said second strand is inhibited. Because the hybridization of said two strands generates covalent base-pairing only between their complementary homology region(s), such specificity increases the targeting efficiency of a gene knock-out system.