 Two types of small ribonucleic acid ( RNA ) molecules – microRNA ( miRNA ) and small interfering RNA ( siRNA ) – are central to RNA interference . RNAs are the direct products of genes , and these small RNAs can bind to other specific messenger RNA ( mRNA ) molecules and either increase or decrease their activity , for example by preventing an mRNA from producing a protein . RNA interference has an important role in defending cells against parasitic nucleotide sequences – viruses and transposons . It also influences development . 
