Trans-acting siRNA

Trans-acting siRNA (abbreviated "TAS", "ta-siRNA" or sometimes "tasiRNA") is a form of small interfering RNA (siRNA) that represses gene expression through post-transcriptional gene silencing in land plants. Ta-siRNAs are transcribed from the genome to form a polyadenylated, double-stranded segment of RNA that gets processed further, resulting in a segment of RNA that is 21-nucleotides long. These segments are incorporated into the RNA-induced Silencing Complex (RISC) and direct the cleavage of target mRNA. ta-siRNAs are termed siRNA because they undergo similar processing and both arise from double-stranded RNA (dsRNA). However, ta-siRNAs differ from other siRNAs in that they bind with less sequence specificity to their targets. They function more like microRNAs because they do not require full sequence complementarity in order to direct cleavage of the target RNA.