Small ANTISENSE RNAs (20 -25 nucleotides) that are generated from specific dsRNAs (RNA, DOUBLE-STRANDED) which trigger targeted mRNA (RNA, MESSENGER) degradation (RNA INTERFERENCE). They serve as guides for the cleavage of homologous mRNA in the RNA-INDUCED SILENCING COMPLEX. The same ribonuclease, Dicer, that is required for processing of the dsRNAs to siRNA is also involved in processing MICRORNAS (miRNAs) from their precursor RNAs.