DICER1 and infection: However, recent studies have demonstrated the production of abundant virus-derived small-interfering RNAs during the infection of undifferentiated and differentiated mammalian cells with distinct positive- or negative-strand RNA viruses, suggesting efficient Dicer processing of virus-derived dsRNAs in mammals.5 How the single human Dicer recognizes and processes dsRNA into siRNA and what cellular cofactors of Dicer mediate this process remains to be resolved.