CD302 and viral infectious disease: For example, DCL1 and DCL4 are required for biogenesis of 21 nt small RNAs that correspond mainly to miRNA and tasiRNA, DCL2 affects accumulation of 21 nt RNA that protects against viral infection and DCL3 acts to produce the 24 nt RNAs that mediate de novo DNA methylation, gene silencing and chromatin modification [19,30].